Method and apparatus at the physical and link layer for mobile communications

ABSTRACT

In a cellular telecommunications network, a mobile communication system to offload data traffic from base stations to small-node devices, includes a radio base station, a plurality of small-node devices, a macro-base-station-to-the-small-node-device (BS2D) communication section configured to receive a first control-plane message from the radio base station over a BS2D communication link, a small-node-device-to-user-equipment (D2UE) communication section configured to transmit user-plane data to a user equipment over a wireless D2UE communication link established responsive to the first control-plane message, and a center small-node device. The center small-node device includes a buffer section, a backhaul communication section configured to receive the user-plane traffic data from a server over a backhaul link, and is configured to manage D2UE connections between the plurality of small-node devices and the mobile station, buffer data to be transmitted in downlink and uplink for the plurality of small-node devices, and conduct a link adaptation for the D2UE connections.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from provisional U.S. PatentApplication No. 61,533,382, filed Sep. 12, 2011, provisional U.S. PatentApplication No. 61,607,901, filed Mar. 7, 2012 and provisional U.S.Patent Application No. 61,616,309, filed Mar. 27, 2012. The contents ofthe priority applications are hereby incorporated by reference in theirentirety.

BACKGROUND OF THE DISCLOSURE

1. Technical Field of the Disclosure

One or more embodiments of the present disclosure relate to theoperation of the Physical and Link Layer design of systems such as thatof 3GPP's Long Term Evolution (LTE). Specifically, the one or moreembodiments focus on the Physical (PHY) and Link Layer design of systemssuch as 3GPP's Long Term Evolution (LTE). A design according to one ormore of the embodiments uses a hybrid Device to UE (D2UE) and Macro toUE (Macro2UE) architecture wherein some functions are maintained by theMacro2UE link and others are supported by the D2UE link.

2. Background Art

One possible way to increase capacity in a wireless network is toincrease the density (number of devices per unit area) of deployedbase-stations or remote antenna units. Hereinafter, such deployed basestation or remote antenna unit is called “small cell unit”. If thedensity of the small-cell units increases, the cell capacity increasesdue to frequency reuse effects. However, there are some difficultiesthat come with increasing the deployment density, especially if suchsmall cell units must be able to operate as conventional base stationson their own.

For example, as the deployment density increases, the number ofhandovers increases because the user equipment changes the serving unit(base station) frequently. As a result, quality of connectivity/mobilityperformance is expected to be degraded.

One possible way to improve the connectivity and mobility is carrieraggregation. That is, conventional carrier aggregation operations of theMacro base station and such small cell units can achieve high-qualityinterworking, because the Macro2UE link can be maintained while UEcommunicates with small-cell units. As a result, network operators canachieve the same quality of connectivity/mobility as the conventionalMacro network.

However, the conventional carrier aggregation operations need to beoperated under the single Macro base station. That is, such small-cellunits have to be remote radio heads or remote antennas which areperfectly controlled by the Macro base station, i.e. cells whereinsmall-cell units provide radio communication services must belong to theMacro base station. From a user data point of view, multiple componentcarriers of the conventional carrier aggregation operations are notvisible to the packet data convergence protocol (PDCP) and radio linkcontrol (RLC) layers, and therefore the Macro base station handles thePDCP/RLC operations for the small-cell units in addition to the Macrocell base station itself. From a physical layer/MAC layer point of view,some cross-carrier operations need to be supported in the conventionalcarrier aggregation operations.

For example, HARQ Acknowledge information for a secondary cell sometimesneeds to be transmitted in a primary cell. Furthermore, physical controlchannel transmitted in a primary cell sometimes notifies the userequipment of the downlink control information for a secondary cell andvice versa in cross-carrier scheduling. That is, very tightinter-working among component carriers is required in the conventionalcarrier aggregation, and so the conventional carrier aggregationoperations need to be operated under the single base station (the singlebaseband processing equipment). In other words, the conventional carrieraggregation operations between the Macro base station and theconventional Pico/Femto base station are impossible, because thePico/Femto base station is a node different from the Macro base station.In the scenarios where remote radio heads or remote antennas which areperfectly controlled by the Macro base station are utilized, signalprocessing complexity of the Macro base station increases as the numberof remote radio heads or remote antennas increases, because centralizedcontrol is conducted by the Macro base station. Such increasingcomplexity results in high cost. As a result, it is difficult to easilyincrease the number of the small-cell units due to high complexity andcost.

In general, the above operations, where remote radio heads or remoteantennas which are perfectly controlled by the Macro base station, arecalled “carrier aggregation of macro cells and remote radio head cells”.The operations are described in Annex J.1 of 36.300, V a.4.0 in 3GPPspecification. The operations are called “RRH CA operation” hereinafter.

The RRH CA operation has the some drawbacks. FIG. 26 illustrates asystem architecture for conventional remote radio head (RRH) CAoperations. In this architecture, a 2 GHz carrier (Macro2UE link)provides macro coverage and remote radio heads (RRHs) are used toimprove throughput at hot spots in a 3.5 GHz carrier (RRH2UE link)Mobility is performed based on the 2 GHz carrier. In this systemarchitecture, one common RLC layer and PDCP layer operation is conductedat Macro base stations (the base station 200A and the base station 200B)for both Macro2UE link and RRH2UE link. Very tight inter-working betweenMacro2UE link and RRH2UE link is also conducted from a physicallayer/MAC layer point of view. This is because the remote radio head isan amplifier, and other operations including, but not limited to,coding/decoding in physical layer and MAC layer operations are conductedin the base station.

As shown in FIG. 27, however, in case that the user equipment 100 islocated on the outside of the base station 200A coverage area, the userequipment 100 cannot be served by the carrier aggregation of the 2 GHzcarrier and the 3.5 GHz carrier. Especially in the case where a new-typecarrier, where common signals such as CRS, PSS/SSS and broadcast signalsare not transmitted, is utilized in the 3.5 GHz carrier, the userequipment 100 cannot be served neither by the base station 200A, nor bythe remote radio head 500A-4, because in general the user equipment 100cannot communicate with the remote radio head 500A-4, which does nottransmit such common signals, without valid connections with the basestation 200A. It is noted that the new type carrier which does notcontain some of common signals or broadcast signals may be called “newcarrier type” or “additional carrier type” in the standardization.

The user equipment 100 can communicate with the base station 200Binstead of the base station 200A in FIG. 27, but it cannot be served bythe carrier aggregation of the 2 GHz carrier served by the base station200B and the 3.5 GHz carrier served by the remote radio head 500A-4.This is because the remote radio head 500A-4 does not belong to the basestation 200B, and the remote radio head 500A-4 and the base station 200Bcannot have a single RLC layer and PDCP layer operation. Furthermore,the remote radio head 500A-4 and the base station 200B cannot have verytight inter-working from a physical layer and MAC layer point of view.

It clearly indicates that the conventional RRH CA operation may becumbersome from a deployment point of view, because network operatorsneed to align the macro cell coverage area with the RRH coverage areavery accurately.

In general, the base station transmits control signals such as broadcastsignals, and the user equipment communicates with the base station afterreceiving the control signals. That is, the user equipment cannottransmit any signals before receiving the control signals. Therefore theuser equipment cannot start communications because the user equipmentcannot camp on the cell, where the base station provides communicationservices, in idle state. That is, the user equipment cannot conductrandom access procedures which are required for the initiation of thecommunications. This is called the principle of “transmit afterreceive”. This concept can prevent the user equipment from transmittingsignals without any control of the network, and therefore unnecessaryinterference can be avoided.

However, control signals such as broadcast signals sometimes cause somebackward compatibility issues. For example, network signaling, which iscalled “AdditionalSpectrumEmission,” is defined in TS 36.331 and inSection 6.2.4 of TS 36.101 in 3GPP specification. When the userequipment receives the network signaling, it must transmit uplinksignals in order to meet additional spectrum emission requirements,which is specified in Section 6.2.4 of TS 36.101. Here, if the userequipment receives unknown network signaling in the control signals, itcannot communicate with the base station, because the user equipment mayviolate regulatory requirements which are related to the unknown networksignaling. Especially in case that the user equipment is in idle state,the user equipment cannot camp on the cell which transmits unknownnetwork signaling and cannot connect to the network. It means that newnetwork signaling cannot be added after the user equipment isdistributed in the market. In other words, if new network signaling isadded after the user equipment is distributed in the market, a backwardcompatibility issue, in which the user equipment cannot communicate withthe base station after that, happens.

SUMMARY OF CLAIMED SUBJECT MATTER

In a cellular telecommunications network, a mobile communication systemto offload data traffic from radio base stations to small-node devicesmay include at least one macro-base-station-to-the-small-node-device(BS2D) communication section in communication with a radio base stationthrough a first link, a plurality of small-node-device-to-user-equipment(D2UE) communication sections in wireless communication with a mobilestation through a second link, a buffer section to buffer data, and abackhaul communication section in communication with a server through athird link. The BS2D communication section may receive, through thefirst link, a first control signal from the radio base station toestablish the second link. The plurality of D2UE communication sectionsmay establish the second link upon receiving the first control signal,where the plurality of D2UE communication sections may receive a firstdata through the second link which is sent by the mobile station to theserver. The backhaul communication section may transmit the first datato the server through the third link, where the backhaul communicationsection may receive a second data which is sent by the server to themobile station, where the plurality of D2UE communication sectionstransmit the second data to the mobile station. The buffer sectionbuffers the first data and the second data for the plurality of D2UEcommunication sections.

A mobile communication system may further include a center small-nodedevice comprising the buffer section and the backhaul communicationsection, and a plurality of small-node devices configured to communicatewith the center small-node device and the mobile station. The centersmall-node device may be configured to manage D2UE connections betweenthe plurality of small-node devices and the mobile station, and bufferdata to be transmitted in downlink and data received in uplink for theplurality of small-node devices. The radio base station may notify thecenter small-node device of identification numbers of each of theplurality of small-node devices in a small-node device group, and thecenter small-node device may select one or more of the plurality ofsmall-node devices in the small-node device group for communication withthe mobile station, and the selection is made based on the quality ofeach associated D2UE connection. The buffer section in the centersmall-node device may include multiple buffer sections; each of theplurality of small-node devices may include one of the plurality of D2UEcommunication sections. The plurality of small-node devices and thecenter small-node device may each include a portion of the plurality ofD2UE communication sections. The plurality of small-node devices mayhandle transmitting/receiving data in form of radio frequency signals,and the center small-node device handles baseband processing, and theplurality of small-node devices may handle processing for physicallayer, MAC layer and RLC layer, and the center small-node device handlesprocessing for PDCP layer and buffering data. At least one of theplurality of D2UE communication sections may transmit the second data tothe mobile station at a time frame, and the first data and the seconddata may be scrambled by a sequence specific to the mobile station inthe second link. Identification numbers of the plurality of D2UEcommunication sections may be included in the first control signal.

In a cellular telecommunication network, a method to offload datatraffic from radio base stations to small-node devices, may includecommunicating with a radio base station through a first link with atleast one macro-base-station-to-the-small-node-device (BS2D)communication section, buffering data with a buffer section,communicating wirelessly with a mobile station through a second linkwith a plurality of small-node-device-to-user-equipment (D2UE)communication sections, communicating with a server through a third linkwith a backhaul communication section, and receiving from the radio basestation through the first link a first control signal to establish thesecond link at the BS2D communication section. The method may alsoinclude establishing the second link upon receiving the first controlsignal at the plurality of D2UE communication sections, receiving at theplurality of D2UE communication sections a first data through the secondlink which is sent by the mobile station to the server, and wherein thebackhaul communication section transmit the first data to the serverthrough the third link, receiving at the backhaul communication sectiona second data which is sent by the server to the mobile station, whereinthe plurality of D2UE communication sections transmit the second data tothe mobile station, and buffering with the buffer section the first dataand the second data for the plurality of D2UE communication sections.

In a cellular telecommunications network, a mobile station to receiveoffloaded data from multiple small-node devices, may include at leastone macro-base-station-to-the-user-equipment (BS2UE) communicationsection to receive both control-plane data and first user-plane datafrom a base station over a wireless BS2UE communication link; and

a small-node-device-to-the-user-equipment (D2UE) communication sectionto receive second user-plane data from a server through a plurality ofsmall-node devices using a wireless D2UE communication link, wherein theBS2UE communication section receives a first control-plane message fromthe base station over the wireless BS2UE communication link, the D2UEcommunication section establishes the wireless D2UE communication linkresponsive to the first control-plane message; and the second user-planedata is scrambled by a sequence specific to the mobile station in thewireless D2UE communication link.

In a cellular telecommunications network, a radio base station tocontrol a user equipment (UE) and a plurality of small-node devices, mayinclude a macro-base-station-to-the-UE (BS2UE) communication sectionexchanges user-plane and first control-plane data with the UE using awireless BS2UE communication link, amacro-base-station-to-the-small-node-device (BS2D) communication sectionexchanges second control-plane data with at least one of the pluralityof small-node devices using a BS2D communication link; and

a D2UE control unit controls an establishment and also arelease/reconfiguration/handover of a small-node-device-to-the-UE (D2UE)communication link through a first control-plane data and/or a secondcontrol-plane data transmitted to at least one of the UE and theplurality of small-node devices using one of the BS2UE and BS2Dcommunication links, wherein data in the D2UE communication link isscrambled by a sequence specific to a mobile station.

In a cellular telecommunications network, a small-node device to offloaddata traffic from radio base stations to the small-node device and acenter-small-node device, may include amacro-base-station-to-the-small-node-device (BS2D) communication sectionin communication with a radio base station through a first link, and asmall-node-device-to-user-equipment (D2UE) communication section inwireless communication with a mobile station through a second link,wherein the BS2D communication section receives, through the first link,a first control signal from the radio base station to establish thesecond link, the D2UE communication section establish the second linkupon receiving the first control signal, the D2UE communication sectionreceive a first data through the second link which is sent by the mobilestation to a server, and wherein the D2UE communication section transmitthe first data to the center-small-node device. Further the small-nodedevice may transmit the first data to the server through the third link,wherein the center-small-node device receives a second data through thethird link which is sent by the server to the mobile station, andwherein the center-small-node device transmits the second data to theD2UE communication section, the D2UE communication section transmits thesecond data to the mobile station through the second link, and thecenter-small-node device buffers the first data and the second data forthe D2UE communication section.

In a cellular telecommunications network, a center-small-node device tooffload data traffic from radio base stations to a plurality ofsmall-node devices and the center-small-node device, may include abuffer section to buffer data and to communicate with a plurality ofsmall-node devices, and a backhaul communication section incommunication with a server through a first link, wherein the pluralityof small-node devices communicate with a mobile station through a secondlink, the plurality of small-node devices receive a first data throughthe second link which is sent by the mobile station to a server, andwherein the plurality of small-node devices transmit the first data tothe buffer section. The backhaul communication section may transmit thefirst data to the server through the third link, wherein the backhaulcommunication section receives a second data which is sent by the serverto the mobile station, and wherein the buffer section transmits thesecond data to the plurality of small-node devices. The small-nodedevices may transmit the second data to the mobile station, and thebuffer section buffers the first data and the second data.

In a cellular telecommunications network, a mobile station to receiveoffloaded data from a small-node device, may include at least onemacro-base-station-to-the-user-equipment (BS2UE) communication sectionto receive both control-plane data and first user-plane data from a basestation over a wireless BS2UE communication link, and asmall-node-device-to-the-user-equipment (D2UE) communication section toreceive second user-plane data from a server through the small-nodedevice using a wireless D2UE communication link, wherein the BS2UEcommunication section receives a first control-plane message from thebase station over the wireless BS2UE communication link. The D2UEcommunication section may establish the wireless D2UE communication linkin response to the first control-plane message, and the D2UEcommunication section may release the wireless D2UE communication linkwhen the radio link failure of the wireless BS2UE communication link isdetected by the BS2D communication section.

In a cellular telecommunications network, a mobile station to receiveoffloaded data from a small-node device, may include at least onemacro-base-station-to-the-user-equipment (BS2UE) communication sectionto receive both control-plane data and first user-plane data from a basestation over a wireless BS2UE communication link, and asmall-node-device-to-the-user-equipment (D2UE) communication section toreceive second user-plane data from a server through the small-nodedevice using a wireless D2UE communication link. The BS2UE communicationsection may receive a first control-plane message from the base stationover the wireless BS2UE communication link, and the D2UE communicationsection may establish the D2UE communication link responsive to thefirst control-plane message. The D2UE communication section may stoptransmitting signals in the wireless D2UE communication link when theradio link failure of the wireless BS2UE communication link is detectedby the BS2D communication section.

Other aspects and advantages of the invention will be apparent from thefollowing description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory view showing a communication system accordingto one or more embodiments of the present disclosure.

FIG. 2 is an explanatory view showing D2UE connection 710, and BS2UEconnection 720, BS2D connection 730, Backhaul connection 740, andBackhaul connection 750 according to one or more embodiments of thepresent disclosure.

FIG. 3 is an explanatory view showing data flow for D2UE connection 710and BS2UE connection 720 according to one or more embodiments of thepresent disclosure.

FIG. 4 is an explanatory view showing a communication system accordingto one or more embodiments of the present disclosure.

FIG. 5 is an explanatory view showing a communication system accordingto one or more embodiments of the present disclosure.

FIG. 6 is an explanatory view showing a communication system accordingto one or more embodiments of the present disclosure.

FIG. 7 is an explanatory view showing a communication system accordingto one or more embodiments of the present disclosure.

FIG. 8 is an explanatory view showing a communication system accordingto one or more embodiments of the present disclosure.

FIG. 9 is an explanatory view showing a communication system accordingto one or more embodiments of the present disclosure.

FIG. 10 is a diagram explaining time division multiplexing for D2UE andMacro2UE transmissions according to one or more embodiments of thepresent disclosure.

FIG. 11 is a functional block diagram of a small-node device accordingto one or more embodiments of the present disclosure.

FIG. 12 is a functional block diagram of a user equipment according toone or more embodiments of the present disclosure.

FIG. 13 is a functional block diagram of a base station according to oneor more embodiments of the present disclosure.

FIG. 14 is a flowchart showing operations in the radio communicationsystem according to one or more embodiments of the present disclosure.

FIG. 14A is a figure showing operations in the radio communicationsystem according to one or more embodiments of the present disclosure.

FIG. 15 is a figure showing operations in the radio communication systemaccording to one or more embodiments of the present disclosure.

FIG. 16 is a figure showing operations in the radio communication systemaccording to one or more embodiments of the present disclosure.

FIG. 17 is a figure showing operations in the radio communication systemaccording to one or more embodiments of the present disclosure.

FIG. 17A is a flowchart showing operations in the radio communicationsystem according to one or more embodiments of the present disclosure.

FIG. 18 is a flowchart showing operations in the radio communicationsystem according to one or more embodiments of the present disclosure.

FIG. 19 is an explanatory view showing interference due to bad mobilitybehaviors according to one or more embodiments of the presentdisclosure.

FIG. 20 is an explanatory view showing a communication system accordingto one or more embodiments of the present disclosure.

FIG. 21 is a flowchart showing operations in the radio communicationsystem according to one or more embodiments of the present disclosure.

FIG. 22 is an explanatory view showing radio resource for the D2UE pilotsignals according to one or more embodiments of the present disclosure.

FIG. 22A is an explanatory view showing time synchronization betweenD2UE link and BS2UE link according to one or more embodiments of thepresent disclosure.

FIG. 22B is an explanatory view showing time synchronization betweenD2UE link and BS2UE link according to one or more embodiments of thepresent disclosure.

FIG. 22C is an explanatory view showing a communication system accordingto one or more embodiments of the present disclosure.

FIG. 22D is an explanatory view showing time synchronization betweenD2UE link and BS2UE link according to one or more embodiments of thepresent disclosure.

FIG. 22E is an explanatory view showing a communication system in whichD2UE pilot signals are transmitted by small-node devices according toone or more embodiments of the present disclosure.

FIG. 22F is an explanatory view showing a physical layer format on theD2UE pilot signal according to one or more embodiments of the presentdisclosure.

FIG. 22G is an explanatory view showing reception of the D2UE pilotsignal in the user equipment 100 according to one or more embodiments ofthe present disclosure.

FIG. 22H is an explanatory view showing delay profile derived from thereceived D2UE pilot signal according to one or more embodiments of thepresent disclosure.

FIG. 23 is a flowchart showing operations in the radio communicationsystem according to one or more embodiments of the present disclosure.

FIG. 24 is a flowchart showing operations in the radio communicationsystem according to one or more embodiments of the present disclosure.

FIG. 25 is a flowchart showing operations in the radio communicationsystem according to one or more embodiments of the present disclosure.

FIG. 25A is a flowchart showing operations in the radio communicationsystem according to one or more embodiments of the present disclosure.

FIG. 26 is an explanatory view showing conventional remote-radio-headbased carrier aggregation operations.

FIG. 27 is an explanatory view showing conventional remote-radio-headbased carrier aggregation operations.

FIG. 27A is an explanatory view showing conventional remote-radio-headbased carrier aggregation operations.

FIG. 28 is an explanatory view showing operations in the hybrid D2UE andBS2UE system according to one or more embodiments of the presentdisclosure.

FIG. 29 is an explanatory view showing a communication system accordingto one or more embodiments of the present disclosure.

FIG. 30 is a functional block diagram of a small-node device and acenter-small-node device according to one or more embodiments of thepresent disclosure.

FIG. 31 is a functional block diagram of a small-node device and acenter-small-node device according to one or more embodiments of thepresent disclosure.

FIG. 32 is a functional block diagram of a small-node device and acenter-small-node device according to one or more embodiments of thepresent disclosure.

FIG. 32A is a functional block diagram of a small-node device and acenter-small-node device according to one or more embodiments of thepresent disclosure.

FIG. 32B is a functional block diagram of a small-node device and acenter-small-node device according to one or more embodiments of thepresent disclosure.

FIG. 33 is a functional block diagram of a small-node device, afunctional block diagram of a center-small-node device, a functionalblock diagram of a user equipment, a functional block diagram of a basestation according to one or more embodiments of the present disclosure.

FIG. 34 is an explanatory view showing DL transmission according to oneor more embodiments of the present disclosure.

FIG. 35 is an explanatory view showing UL transmission according to oneor more embodiments of the present disclosure.

FIG. 36 is an explanatory view showing a communication system accordingto one or more embodiments of the present disclosure.

FIG. 37 is an explanatory view showing a communication system accordingto one or more embodiments of the present disclosure.

DETAILED DESCRIPTION

In embodiments of the invention, numerous specific details are set forthin order to provide a more thorough understanding of the invention.However, it will be apparent to one with ordinary skill in the art thatthe invention may be practiced without these specific details. In otherinstances, well-known features have not been described in detail toavoid obscuring the invention.

One or more embodiments of the present disclosure relate generally to asystem concept, and physical and link layer design, to allow forincreasing the cell capacity by increasing the small-cell units at lowcost/complexity and without the above drawbacks, such asconnectivity/mobility issues, issues in carrier aggregation operations,and backward compatibility issues. This invention will be particularlywell suited to deployments with large carrier frequencies with verylarge densities (very small cells).

The system concept is a low cost hybrid D2UE and BS2UE system whichallows D2UE connections to be opportunistically used to offload trafficfrom the Macro System (BS2UE system). Here, Macro corresponds to Macrobase station. High density and low cost/complexity are achieved by thedeployment of inexpensive “Small Node” devices which supports the D2UEconnections. The small-node device may be regarded as a femto/pico basestation with which the mobile station (i.e., user equipment)communicates simultaneously with communicating with the macro basestation. It is noted that it is impossible for the user equipment tocommunicate with a femto/pico base station simultaneously with the macrobase station using the conventional carrier aggregation operations,because the Pico/Femto base station is a node different from the Macrobase station as mentioned above.

Each of these small-node devices conducts offloading for the Macro2UE(BS2UE) system by the D2UE link. The concept of offloading is explainedas follows:

Each of these small-node devices has a backhaul connection, which isconnected to the Internet or the core network, communicates with aserver in the Internet or the core network, and transfers some of data,which should be transferred between UE and a server, utilizing thebackhaul link and the D2UE connections. For example, according to one ormore embodiments of the present disclosure, best effort packets, such asweb browsing data, e-mail data, and the like, are transferred in theD2UE connections, and control signaling, such as RRC messages, NASmessages and the like, or Voice packets are transferred in the BS2UEconnections.

The D2UE connections are controlled by the Macro base station. Morespecifically, basic radio resource control, such as connectionestablishment, handover, connection release, call admission control andthe like, for the D2UE connections are controlled by the Macro basestation. Furthermore, the BS2UE connections between UE and the Macrobase station are maintained while the D2UE connections are configured.

As a result, high quality interworking between Macro2UE (BS2UE) and D2UEconnections are achieved, and data offloading can be conducted in thesmall-node devices. Because the signal processing for the data in theD2UE connections are conducted by the small-node devices, instead of theMacro base station, the complexity/cost of the Macro base station can bereduced.

Furthermore, the signal processing for the data in the D2UE connectionsis conducted by the small-node device which is different from the Macrobase station, and therefore the scenario illustrated in FIG. 27 does nothappen because the user equipment 100 can more flexibly select thesmall-node device irrespective of the serving Macro base station, asillustrated in FIG. 28. It means that network operators does not have toalign the macro cell coverage area with the small-node coverage areavery accurately and that efforts for small cell deployment can bereduced in the hybrid D2UE and BS2UE system.

Furthermore, the small-node device does not transmit the control signalssuch as broadcast signals, because they are transmitted by the macrobase station. As a result, the aforementioned backward compatibilityissues can be reduced because the macro base station can determinewhether or not the user equipment can communicate with the small-nodedevice based on the user equipment information, such as its version orits release.

A feature of one or more embodiments of the invention is that the HybridD2UE and Macro2UE (BS2UE) system that offloads Macro Traffic at a lowcost and complexity. Another feature is that a small-node device has abackhaul link with a server and a D2UE link with UE, and transfer data,which should be transferred between the server and the UE, via thebackhaul link and the D2UE link. Additionally, the D2UE connections arecontrolled by the Macro. Further, a protocol design for associating a UEto a small-node device and a physical layer design supporting D2UEconnections may also be included.

One technical advantage of one or more embodiments of the invention isachieving effectively high deployment density at low cost. High densityhas benefits in increased capacity and improved channel conditions.

The system is robust. Note, the Macro2UE (BS2UE) connection ismaintained by the macro and is always a backup to the D2UE connection.Furthermore, high-quality interworking between the Macro2UE and the D2UEconnections is possible because the D2UE connection is controlled by theMacro.

For remote radio heads or remote antennas which are controlled by theMacro base station, as the number of remote radio heads or remoteantennas increases, signal processing complexity in the Macro basestation increases because the Macro base station needs to handle U-planedata transmitted/received by the remote radio heads or remote antennas.In one or more embodiments of the invention, however, the Macro basestation does not have to handle the U-plane data transmitted in the D2UEconnection, and the U-plane data handling can be shared by a lot ofsmall-node devices. That is, distributed control can be achieved by thehybrid Macro2UE (BS2UE) and D2UE system. Therefore, the complexity ofthe Macro base station can be minimized.

The signal processing for the data in the D2UE connection is conductedby the small-node device which is different from the Macro base station.As a result, the user equipment 100 can more flexibly select thesmall-node device irrespective of the Macro base station. It means thatnetwork operators do not have to align the macro cell coverage area withthe small-node coverage area very accurately and that efforts for smallcell deployment can be reduced in the hybrid D2UE and BS2UE system.

The small-node device does not transmit the control signals such asbroadcast signals, because they are transmitted by the macro basestation in a macro base station frequency carrier different from thesmall-node device frequency carrier. As a result, the aforementionedbackward compatibility issues can be reduced because the macro basestation can determine whether or not the user equipment can communicatewith the small-node device based on the user equipment information, suchas its version or its release.

Therefore, according to one or more embodiments of the invention, it ispossible to provide a radio communication system for enabling highcapacity, high connectivity, low costs and low planning complexity.

One option to increase capacity in a wireless network is to increase thedensity (number of devices per unit area) of deployed base-stations orremote antenna units. Hereinafter, such deployed base station or remoteantenna unit is called “small cell unit”. If the density of thesmall-cell units increases, the cell capacity increases due to frequencyreuse effects. However, there are some difficulties that come withincreasing the deployment density, especially if such small cell unitsmust be able to operate as conventional base stations on their own.

One or more embodiments of the invention relate to a system concept, andphysical and link layer design, to allow for increasing the cellcapacity by increasing the deployment density at low cost andcomplexity. It may be particularly well suited to deployments with largecarrier frequencies with very large densities (very small cells).

The system concept is a low cost hybrid D2UE and BS2UE system whichallows D2UE connections to be opportunistically used to offload trafficfrom the Macro System. High density and low cost/complexity are achievedby the deployment of small-node devices. Here, the user equipmentcommunicates with the small-node device, while the user equipmentsimultaneously communicates with the macro base station. That is, theBS2UE connection is maintained while the data offloading is conducted inthe D2UE connection. It is also noted that the small-node device is anode different from the macro base station and therefore conventionalcarrier aggregation operations cannot be conducted between the macrobase station and the small-node device.

Each of these small-node devices will provide a D2UE link to UE in orderto offload the traffic generated by UE. The concept of offloading isexplained as follows:

Each of these small-node devices has a backhaul connection, which isconnected to the Internet or the core network, and it communicates witha server in the Internet or the core network, and transfers some of thedata, which should be transferred between UE and a server, utilizing thebackhaul link and the D2UE connections. For example, according to one ormore embodiments of the present disclosure, best effort packets, such asweb browsing data, e-mail data, and the like, are transferred in theD2UE connections, and control signaling, such as RRC messages, NASmessages and the like, or Voice packets are transferred in the BS2UEconnections.

The D2UE connections are controlled by the Macro base station. Morespecifically, basic radio resource control, such as connectionestablishment, handover, connection release, call admission control andthe like, for the D2UE connections are controlled by the Macro basestation. Furthermore, the BS2UE connections between UE and the Macrobase station are maintained while the D2UE connections are configured.

A small-node device supports some sets of functionality in order tosupport D2UE transfer of data in terms of D2UE link. A D2UE connectionmay be similar to a D2D connection.

The small-node device supports Macro2D (BS2D) link and the D2UE link iscontrolled by Macro. In terms of UE, UE supports Macro2UE (BS2UE) linkand the D2UE link is controlled by Macro as well. Control signaling forthe D2UE connections can be transmitted to the UE via the Macro2UEconnection, and another control signaling for the D2UE connections canbe transmitted to the small-node device via the Macro2D (BS2D)connection.

In addition to the D2UE link, the small-node device supports a backhaullink, such as wired connection to the Internet or the core network. Thebackhaul link is not limited to the wired connection to the Internet orthe core network, but may be wireless connection including WiFi andcellular system, but not limited to, to the Internet or the corenetwork.

To achieve high quality connectivity, more important functions such asRRC connection state control and NAS control are maintained by theMacro2UE (BS2UE) link. Control for radio interface of D2UE connectionsis conducted by the Macro2D (BS2D) and the Macro2UE (BS2UE). The controlmay include, but is not limited to, at least one of connectionestablishment, connection management, connection reconfiguration,handover, connection release, radio resource selection management, powercontrol, link adaptation, call admission control, radio bearerassignment, traffic measurement, radio measurement control, bearermanagement, security association and so on.

In some embodiments, D2UE and Macro2UE (BS2UE) transmissions can operatein different bands exploiting Carrier Aggregation Functions in terms ofRadio Frequency (RF) components. The Carrier Aggregation Functions of RFcomponents means a function in which the transmitter can transmitsignals and the receiver can receive signals in more than one carriersimultaneously. D2UE transmissions can operate in one band, and Macro2UE(BS2UE) transmissions can operate in another band, simultaneously intime.

In some embodiments, D2UE and Macro2UE (BS2UE) transmissions can operatein different bands exploiting time division multiplexing functions,wherein the D2UE transmission occur only at selected time and theMacro2UE (BS2UE) transmissions occur at the remaining time.

A radio communication system according to one or more embodiments of theinvention will be described with reference to FIGS. 1 and 2.

A radio communication system (mobile communication system) 1000 includesa base station 200, a plurality of user equipment (UE, or referred to asa mobile station) 100 (100 ₁, 100 ₂, 100 ₃, . . . , 100 n, n is aninteger where n>0), and a plurality of small-node devices 500 (500 ₁,500 ₂, 500 ₃, . . . , 500 _(m), m is an integer where m>0).

FIG. 2 illustrates a connection between the small-node device 500 andthe user equipment 100 (D2UE connection 710), a connection between thebase station 200 and the user equipment 100 (BS2UE connection 720), anda connection between the base station 200 and the small-node device 500(BS2D connection 730). The D2UE connection 710 may be called a D2UElink. The BS2UE connection 720 may be called a BS2UE link. The BS2Dconnection 730 may be called a BS2D link.

In FIG. 2, backhaul connections are also illustrated, i.e. a backhaulconnection between the base station 200 and access gateway apparatus(Backhaul connection 740) and a backhaul connection between thesmall-node device 500 and core network (CN) 400 (Backhaul connection750) are shown. As described later, the backhaul connection 750 may be aconnection between the small-node device 500 and the base station 200,or a connection between the small-node device 500 and the access gatewayapparatus 300, instead of the connection between the small-node device500 and the core network 400. The backhaul connection 740 may be calledBackhaul link 740. The backhaul connection 750 may be called Backhaullink 750.

In the following description, the user equipment 100 (100 ₁, 100 ₂, 100₃, . . . , 100 n) has the same configuration, function and state, and isdescried as the user equipment 100 below to give an explanation unlessotherwise specified.

In the following description, the small-node device 500 (500 ₁, 500 ₂,500 ₃, . . . , 500 m) has the same configuration, function and state,and is descried as the small-node device 500 below to give anexplanation unless otherwise specified.

The base station 200 communicates with the user equipment 100 in a cell50 utilizing Evolve UTRA and UTRAN (alias: Long Term Evolution (LTE)) inthe BS2UE link. It is noted that the communication system between thebase station 200 and the user equipment 100 may not be limited to LTE.The communication system may include, but is not limited to, LTEAdvanced or WiMAX or WiFi or any other system. The communication systemmay use Frequency Division Duplex (FDD) or Time Division Duplex (TDD).

The base station 200 is connected to a higher layer station, forexample, according to one or more embodiments of the present disclosure,access gateway apparatus 300 in the backhaul connection 740, and theaccess gateway apparatus 300 is connected to a core network (CN) 400.The access gateway may be also referred to as MME/SGW (MobilityManagement Entity/Serving Gateway). A server 600 may also be connectedto the core network 400.

The base station 200 is connected to the small-node device 500 in theBS2D connection 730.

The small-node device 500 communicates with the base station 200 in acell 50 utilizing BS2D connection 730. For example, according to one ormore embodiments of the present disclosure, an X2 link defined in 3GPPmay apply to the BS2D connection 730. Alternatively, an enhancement ofthe X2 link may apply to the BS2D connection 730. Alternatively, a wiredor wireless link, which is different from the X2 link, may apply to theBS2D connection 730.

Alternatively, a LTE link may apply to the BS2D connection 730. In thiscase, the small-node device 500 may behave as user equipment when itcommunicates with the base station 200 and may behave as base stationwhen it communicates with the user equipment 100.

The small-node device 500 communicates with the user equipment 100utilizing D2UE connection 710. A LTE link or a simplified LTE linkapplies to the D2UE connection 710. That is, the small-node device 500communicates with the user equipment 100 utilizing the LTE link or thesimplified LTE link in the D2UE connection 710. It is noted that thecommunication system between the small-node device 500 and the userequipment 100 is not limited to LTE. The communication system may be LTEAdvanced or WiMAX or WiFi or any other system. The system may use FDD,or TDD.

The small-node device 500 is connected to the core network (CN) 400 inthe backhaul connection 750.

The user equipment 100 communicates with the base station 200 in theBS2UE connection 720 and communicates with the small-node device 500 inthe D2UE connection 710.

FIG. 3 illustrates data flow in the radio communication system. Data #1is transferred from the access gateway apparatus 300 to the base station200 in the backhaul connection 740 and then transmitted to the userequipment 100 in the BS2UE connection 720 in downlink (DL), and viceversa in uplink (UL). It is the same as data flow in a conventionalradio communication system. In addition to Data #1, Data #2 istransferred from the core network 400 to the small-node device 500 inthe backhaul connection 750 and then transmitted to the user equipment100 in the D2UE connection 710 in DL, and vice versa in UL, for offloadpurpose. Control signaling for D2UE connection 710 is transmitted in theBS2D connection 730 so that the base station 200 can controlcommunication in the D2UE connection 710. Control signaling for D2UEconnection 710 is transmitted also in the BS2UE connection 720 so thatthe base station 200 can control the communication in the D2UEconnection 710. The control signaling in the BS2UE connection 720 may beradio resource control (RRC) signaling. More specifically, Data #1 maybe RRC signaling, NAS signaling, Voice packets and the like, and Data #2may be best effort packets, FTP data, Web browsing packets and the like.That is, it may be determined by data bearers what kinds of data aretransferred as Data #1 or Data #2. As a result, connectivity can bemaintained by the BS2UE connection 720, and simultaneously U-plane dataoffload can be achieved in the D2UE connection 710.

It is noted that the small-node device 500 is a node different from thebase station 200, and therefore the radio communication system cannotuse a conventional carrier aggregation. The base station 200 does nothave to process coding, decoding, modulation, demodulating and the likefor the U-plane data (Data #2), and therefore complexity for the basestation 200 can be reduced, compared to the conventional carrieraggregation.

It is also noted that Data #1 is transferred between the small-nodedevice 500 and the core network 400 for offload purpose, and thereforethe radio communication system is different from conventional softhandover. Furthermore, the BS2UE connection 720 uses a frequency carrierdifferent from the one utilized in the D2UE connection 710, andtherefore the radio communication system is different from conventionalsoft handover. Furthermore, there is no difference between two links inthe conventional soft handover, but the D2UE connection 710 is differentfrom the BS2UE connection 720, in terms of radio bearers conveyed ineach connection and connection control handling.

According to the above mentioned hybrid D2UE and BS2UE system, networkoperators can easily increase the number of small-node devices withoutincreasing signal processing complexity in the base station 200, and asa result they can increase the cell capacity.

There may be various embodiments for system architecture of the radiocommunication system. For example, according to one or more embodimentsof the present disclosure, the small-node device 500 is connected to thecore network (CN) 400 in the backhaul connection 750 in FIG. 1, but itmay be connected to the Internet 410 in the backhaul connection 750, asshown in FIG. 4. That is, the small-node device 500 may be connected toa server 610 via the Internet 410, instead of being connected to theserver 600 via the core network 400. In the radio communication systemillustrated in FIG. 4, the core network 400 may be regarded as a networkcontrolled by a network operator. The core network 400 may include MME,S/P-GW, Node for billing system, HLS (database for customers) and thelike.

Alternatively, as illustrated in FIG. 5, the system may be a mixture ofFIG. 1 and FIG. 4. The small-node device 500 may be connected to theserver 600 via the core network 400 or to the server 610 via theInternet 410 in the backhaul connection 750. It may be determined bydata bearers whether data should be transferred via the small-nodedevice 500 and the Internet 410 or via the small-node device 500 and thecore network 400. The data bearers may be logical channels or logicalchannel types.

Alternatively, as illustrated in FIG. 6, the small-node device 500 maybe connected to the gateway apparatus 310 in the backhaul connection750, and the gateway apparatus 310 may be further connected to the corenetwork 400 or the Internet 410. The gateway apparatus 310, which thesmall-node device 500 communicates with, may be a gateway, which isspecifically deployed for connection with the small-node 500.Alternatively, as illustrated in FIG. 7, the small-node device 500 maybe connected to the gateway apparatus 300 in the backhaul connection750, similarly to the base station 200.

Alternatively, as illustrated in FIG. 8, the small-node device may beconnected to the base station 200 in the backhaul connection 750. Inthis case, the BS2D connection 730 may be the same as the backhaulconnection 750.

Alternatively, as illustrated in FIG. 9, the small-node device 500 maybe connected to a center-small-node device 510, and thecenter-small-node device 510 may be connected to the core network 400 orthe Internet 410 via the gateway apparatus 310. The gateway apparatusmay be omitted. The protocol layers may be shared by thecenter-small-node device 510 and the small-node device 500. For example,according to one or more embodiments of the present disclosure, thecenter-small-node device 510 may handle RLC/PDCP layer and thesmall-node device 500 may handle Physical/MAC layer. Other methods toshare the layers may be applicable. This architecture will be describedin details later.

That is, the user equipment 100 has a capability of communicating withthe base station 200 utilizing LTE (the BS2UE connection 720)simultaneously with communicating with the small-node device 500utilizing the D2UE connection 710. The base station 200 is a nodedifferent from the small-node device 500, the D2UE connection 710 iscontrolled by the base station 200 and some data is transferred in theBS2UE connection 720 and others are transferred in the D2UE connection710 for offload purposes.

The small-node device 500 has a capability of communicating with theuser equipment 100 utilizing the D2UE connection 710, a capability ofcommunicating with the base station 200 utilizing the BS2D connection730, a capability of communicating with the core network 400 utilizingthe backhaul connection 750. The base station 200 is a node differentfrom the small-node device 500, the D2UE connection 710 is controlled bythe base station 200 and some of data, which is transferred between theuser equipment 100 and the server 600, is transferred in the D2UEconnection 710 for offload purposes.

The base station 200 has a capability of communicating with the userequipment 100 utilizing the BS2UE connection 720, a capability ofcontrolling the D2UE connection 710 utilizing the BS2UE connection 720and the BS2D connection 730, and a capability of communicating with theaccess gateway apparatus 300 and the core network 400 utilizing thebackhaul connection 740. The base station 200 is a node different fromthe small-node device 500, and some data is transferred in the BS2UEconnection 720 and others are transferred in the D2UE connection 710 foroffload purpose.

The carrier frequency in the D2UE connection 710 may be different fromthe one in the BS2UE connection 720. Alternatively, the carrierfrequency in the D2UE connection 710 may be the same as the one in theBS2UE connection 720.

In some embodiments of the present invention, it is assumed that thecarrier frequency in the D2UE connection 710 is 3.5 GHz. TDD applies tothe D2UE connection 710. Furthermore, it is also assumed that thecarrier frequency in the BS2UE connection 720 is 2 GHz. FDD applies tothe BS2UE connection 720.

In other embodiments, carrier frequency other than 3.5 GHz may be usedin the D2UE connection 710 and carrier frequency other than 2 GHz may beused in the BS2UE connection 720. Furthermore, FDD may be used in theD2UE connection 710 or TDD may be used in the BS2UE connection 720 inother embodiments.

When the user equipment 100 communicates with the server 600, the basestation 200 configures the D2UE connection 710 in addition to the BS2UEconnection 720 so that some of data to be transferred between the userequipment 100 and the server 600 can be offloaded.

More detailed examples, according to one or more embodiments of thepresent disclosure, for configuring the BS2UE connection 720 and theD2UE connection 710 are shown below. First, the user equipment 100 sendsan RRC connection request to the base station 200 at the beginning ofthe communication, and the base station 200 configures the BS2UEconnection 720. Alternatively, the base station sends a paging signal tothe user equipment 100, the user equipment 100 sends an RRC connectionrequest corresponding to the paging signal to the base station 200, andthe base station 200 configures the BS2UE connection 720. Then, the basestation 200 configures the connection between the user equipment 100 andthe server 600 via the base station 200, the access gateway apparatus300, and the core network 400.

The BS2D connection 730 is always configured between the base station200 and the small-node device 500.

Alternatively, the base station 200 may configure the BS2D connection730 in some embodiments, similarly to the BS2UE connection 720 describedabove. That is, the small-node device 500 may have the ability topower-down or enter a sleep state when not in use. The base station 200may be able to send the small-node device 500 a signal to wake up overwireless network. Alternatively, the base station 200 may be able tosend the small-node device 500 the signal to wake up over wired networkand configure BS2D connection 730, instead of the wireless network. Thismay be supported by a protocol design in the BS2D connection 730. Morespecifically, the protocol design may be X2 interface or another kind ofinterface.

In some other embodiments, the protocol design may be LTE interface.Furthermore, the small-node device may be able to use power-savingmodes, such as stand-by modes, equivalent to user equipment. In thiscase, exiting such power-saving modes may be done in the same fashion asthe user equipment 100 and possibly in response to signals expected orsent by the base-station 200. The signals may be a paging signal or acontrol signaling such as MAC control signaling or physical layersignaling.

Alternatively, the BS2D connection 730 may be always configured betweenthe base station 200 and the small-node device 500, and the small-nodedevice 500 may be in a discontinuous reception mode in the BS2Dconnection 730, when the D2UE connection 710 is not configured betweenthe small-node device 500 and the user equipment 100. In this case, thesmall-node device 100 may not transmit signals or may transmit signalsextremely infrequently when the D2UE connection 710 is not configuredbetween the small-node device 500 and the user equipment 100. Forexample, according to one or more embodiments of the present disclosure,even when the D2UE connection 710 is not configured between thesmall-node device 500 and the user equipment 100, the small-node device500 may transmit only pilot signals infrequently so that the userequipment 100 can detect the small-node device 500. The periodicity ofthe pilot signals may be for example 100 ms or 1 second or 10 seconds.Alternatively, even when the D2UE connection 710 is not configuredbetween the small-node device 500 and the user equipment 100, thesmall-node device 500 may transmit pilot signals based on a request fromthe base station 200 so that the user equipment 100 can detect thesmall-node device 500.

Secondly, the base station 200 orders for the user equipment 100 toconfigure the D2UE connection 710, using control signaling in the BS2UEconnection 720. Furthermore, the base station 200 may order for thesmall-node device 500 to configure the D2UE connection 710, usingcontrol signaling in the BS2D connection 730. Configuring the D2UEconnection 710 may be called establishing the D2UE connection 710.

Furthermore, the base station 200 controls the D2UE connection 710. Forexample, according to one or more embodiments of the present disclosure,the base station 200 may order for the user equipment 100 and thesmall-node device 500 to reconfigure or re-establish the D2UE connection710. The base station 200 may order for the user equipment 100 and thesmall-node device 500 to release the D2UE connection 710. The basestation 200 may order for the user equipment 100 to change the D2UEconnection 710 to the one with other small-node device. That is, thebase station 200 may order for the user equipment 100 to conduct thehandover to the other small-node device in a carrier, in whichcommunication in the D2UE connection 710 is conducted. The base station200 may control the above procedures utilizing RRC signaling in theBS2UE connection 720. The base station 200 may control the aboveprocedures utilizing the control signaling in the BS2D connection 730.

Furthermore, when the D2UE connection 710 is dropped, the base station200 may maintain the communications between the user equipment 100 andthe server 600 utilizing the BS2UE connection 720.

Furthermore, the base station 200 may control radio resource for theD2UE connection 710. The details of the radio resource control for theD2UE connection 710 are shown below. Alternatively, the small-nodedevice 500 may control the radio resource for the D2UE connection 710.Alternatively, the radio resource for the D2UE connection 710 may becontrolled by both the base station 200 and the small-node device 500.

The base station 200 configures one or more radio bearers for thecommunications. Control signaling for configuring the radio bearers istransmitted to the user equipment 100 in the BS2UE connection 720.Control signaling for configuring the radio bearers is transmitted tothe small-node device 500 in the BS2D connection 730.

The radio bearer may be called a logical channel. The base station 200configures radio bearers for the BS2UE connection 720 and radio bearersfor the D2UE connection 710. The radio bearers for the BS2UE connection720 may be the same as the ones for the D2UE connection 710.Alternatively the radio bearers for the BS2UE connection 720 may bedifferent from the ones for the D2UE connection 710.

For example, according to one or more embodiments of the presentdisclosure, radio bearers for packets of non-real-time services, such asweb browsing, e-mail, and FTP, may be configured in the D2UE connection710. Radio bearers for packets of real-time services, such as VoIP andstreaming, may be configured in the BS2UE connection 720.

Alternatively, the radio bearers for the packets of non-real-timeservices are configured both in the D2UE connection 710 and in the BS2UEconnection 720, and the packets of non-real-time services may betransmitted preferentially in the D2UE connection 710.

Alternatively, the radio bearers for the packets of real-time servicesare configured both in the D2UE connection 710 and in the BS2UEconnection 720, and the packets of real-time services may be transmittedpreferentially in the BS2UE connection 720. Alternatively, the packetsof real-time services may also be transmitted preferentially in the D2UEconnection 710.

Such prioritization or priority for the packets may be configured by thebase station 200. That is, the base station 200 may configure for eachradio bearer which connection, the D2UE connection 710 or the BS2UEconnection 720, should be preferentially utilized.

C-plane signaling, such as NAS signaling and RRC signaling, may betransmitted in the BS2UE connection 720. For example, according to oneor more embodiments of the present disclosure, RRC signaling includessignaling messages for RRC connection establishment, initial securityactivation, RRC connection reconfiguration, RRC connection release, RRCconnection re-establishment, Radio resource configuration, measurementreport, Handover command and so on. A radio bearer for C-plane signalingmay be called Signaling radio bearer.

In some embodiments, C-plane signaling may be transmitted also in theD2UE connection 710.

Alternatively, one part of data for one radio bearer may be transmittedin the D2UE connection 710 and the other part of the data for the oneradio bearer may be transmitted in the BS2UE connection 720.

The small-node device 500 may transmit common channels/common signals,such as Primary Synchronization signals (PSS), Secondary Synchronizationsignals (SSS), Common Reference Signals, Broadcast channels and thelike, in the D2UE connection 710. Alternatively, the small-node device500 may not transmit any common channels/signals or may transmit commonchannels/signals extremely infrequently. For example, according to oneor more embodiments of the present disclosure, the small-node device 500may transmit pilot signals infrequently so that the user equipment 100can detect the small-node device 500. The periodicity of the pilotsignals may be, for example, 1 second or 10 seconds. Alternatively, thesmall-node device 500 may transmit pilot signals based on a request fromthe base station 200 so that the user equipment 100 can detect thesmall-node device 500.

The user equipment 100 conducts communication in the D2UE connection 710and communication in the BS2UE connection 720 simultaneously. The userequipment 100 may have two sets of radio frequency devices to conductcommunication in the D2UE connection 710 and communication in the BS2UEconnection 720 simultaneously. In other words, the user equipment 100conducts communication in the D2UE connection 710 and communication inthe BS2UE connection 720 simultaneously utilizing carrier aggregationfunctions (simultaneous transmissions and receptions in two carriers).

Alternatively, the user equipment 100 may conduct communication in theD2UE connection 710 and communication in the BS2UE connection 720 in atime division multiplexing manner. For example, according to one or moreembodiments of the present disclosure, two sets of time durations,Duration #A and Duration #B, are defined as shown in FIG. 10, and theuser equipment 100 may conduct the communication in the BS2UE connection720 in one set of the time durations (Duration #A in FIG. 10) and mayconduct the communication in the D2UE connection 710 in the other set ofthe time durations (Duration #B in FIG. 10). The time duration for theD2UE connection 710 may be larger than the one for the BS2UE connection720 so that the data offload effects can be increased. For example,according to one or more embodiments of the present disclosure, thelength of Duration #A may be 8 msec (milliseconds), and the length ofDuration #B may be 1.28 sec.

The time duration for the BS2UE connection 720 (Duration #A in FIG. 10)may correspond to on-duration in DRX control in the BS2UE connection720. The time duration for the D2UE connection 710 may correspond tooff-duration in DRX control in the BS2UE connection 720. Theoff-duration means a sleep mode in DRX control, in which the userequipment 100 does not have to monitor physical control channelstransmitted from the base station 200 in the BS2UE connection 720.

In case that the user equipment 100 conducts communication in the D2UEconnection 710 and communication in the BS2UE connection 720 in a timedivision multiplexing manner, it does not have to support a capabilityof simultaneously communicating both in the D2UE connection 710 and inthe BS2UE connection 720, i.e. it can switch the radio frequency devicefrom the BS2UE connection 720 to the D2UE connection 710 and vice versa.As a result, the cost and complexity of the user equipment 100 can bereduced.

The base station 200 may control the radio resource for the D2UEconnection 710. The radio resource may consist of at least one of timeresource, frequency resource and code resource.

For example, according to one or more embodiments of the presentdisclosure, the base station 200 may configure the frequency resource inthe D2UE connection 710. More specifically, the base station 200 mayconfigure center frequency of a carrier used in the D2UE connection 710.The base station 200 may configure the frequency resource in the D2UEconnection 710 so that it does not overlap with frequency resourceutilized in other small-node devices. As a result, interference in thecarrier used in the D2UE connection 710 can be mitigated.

For example, according to one or more embodiments of the presentdisclosure, the base station 200 may configure the time resource in theD2UE connection 710, which does not overlap with time resource utilizedin other small-node devices. As a result, interference in the D2UEconnection 710 can be mitigated.

For example, according to one or more embodiments of the presentdisclosure, the base station 200 may configure the code resource in theD2UE connection 710, which does not overlap with code resource utilizedin other small-node devices. As a result, interference in the D2UEconnection 710 can be mitigated.

It may be noted that some parameters of the radio resource for the D2UEconnection 710 may be configured by the base station 200 and the otherparameters may be configured by the small-node device 710. Morespecifically, the frequency domain resource for the D2UE connection 710may be configured by the base station 200 and the time domain resourcefor the D2UE connection 710 may be configured by the small-node device500. Alternatively, the center carrier frequency for the D2UE connection710 may be configured by the base station 200 and the other frequencydomain resource, such as identification number of resource blocks, thenumber of resource blocks and the like, and the time domain resource forthe D2UE connection 710 may be configured by the small-node device 500.

Alternatively, the base station 200 may configure several sets of theradio resource for the D2UE connection 710, and the small-node device500 may configure one out of the several sets of the radio resource forthe D2UE connection 710.

The base station 200 transmits control signaling to the user equipment100 in the BS2UE connection 720 so that it configures the radio resourcefor the D2UE connection 710 as described above. Furthermore, the basestation 200 transmits control signaling to the small-node device 500 inthe BS2D connection 730 so that it configures the radio resource for theD2UE connection 710 as described above.

The base station 200 controls transmission power for DL in the D2UEconnection 710. More specifically, the base station 200 may configurethe maximum transmission power for DL in the D2UE connection 710.Furthermore, the base station 200 controls transmission power for UL inthe D2UE connection 710. More specifically, the base station 200 mayconfigure the maximum transmission power for UL in the D2UE connection710.

The base station 200 may set the maximum transmission power for DL or ULin the D2UE connection 710 based on the number of the user equipment 100in the cell where the small-node device 500 provides radio communicationservice. For example, according to one or more embodiments of thepresent disclosure, the base station 200 sets the maximum transmissionpower to be higher in case that the number of the user equipment 100 inthe cell is relatively small. As a result, in case that there are a lotof user equipment 100, interference level in the carrier used in theD2UE connection 710 can be reduced by making the maximum transmissionpower low. In case that there is not a lot of user equipment, coveragearea of the D2UE connection 710 can be increased by making the maximumtransmission power high.

Alternatively, the base station 200 may set the maximum transmissionpower in the D2UE connection 710 based on the frequency wherecommunications in the D2UE connection 710 are conducted. Morespecifically, in case that the frequency where the communications in theD2UE connection 710 are conducted is closed to the one which is utilizedby other system, interference level with the system can be reduced bymaking the maximum transmission power low. In case that the frequencywhere the communications in the D2UE connection 710 are conducted is notclosed to the one which is utilized by other system, coverage area ofthe D2UE connection 710 can be increased by making the maximumtransmission power high.

The user equipment 100 has a capability of making measurements anddetecting the nearest small-node device 500 so that the data throughputin the D2UE connection 710 can be maximized and the interference causedby the D2UE connection 710 can be minimized. Furthermore, the userequipment 100 has a capability of reporting results of the measurementsand the detected nearest small-node device to the base station 200. Thebase station controls the D2UE connection 710 based on the results andthe detected nearest small-node device, which are reported by the userequipment 100. For example, according to one or more embodiments of thepresent disclosure, when the nearest small-node device is changed, thebase station 200 may order for the user equipment to stop communicationswith currently serving small-node device, and start new communicationwith the nearest small-node device, which is newly detected.

The small-node device 500 according to this embodiment will be describedwith reference to FIG. 11.

The small-node device 500 according to this embodiment has a BS2Dcommunication section 502, D2UE communication section 504, and aBackhaul communication section 506. The BS2D communication section 502,the D2UE communication section 504, and the Backhaul communicationsection 506 are connected to each other.

The BS2D communication section 502 communicates with the base station200 utilizing the BS2D connection 730.

More specifically, the BS2D communication section 502 receives controlsignaling for the D2UE connection 710 from the base station 200, andtransmits control signaling for the D2UE connection 710 to the basestation 200. The control signaling includes signaling forestablishing/configuring/re-configuring/re-establishing/releasing theD2UE connection 710. Signaling for D2UE connection handover may also beincluded in the control signaling. The control signaling is transmittedto the D2UE communication section 504.

As described above, the LTE link may apply to the BS2D connection 730.In this case, the control signaling may be RRC layer signaling in LTE.Alternatively, the control signaling may be MAC layer signaling in LTE.Alternatively, some of the control signaling may be RRC signaling andothers may be MAC layer signaling.

The control signaling may include parameters for at least one ofphysical layer, MAC layer, RLC layer, PDCP layer, or RRC layer in theD2UE connection 710. The control signaling may include information forthe radio bearers in the D2UE connection 710.

Furthermore, the control signaling may include information of radioresource control for the D2UE connection 710. As described above, theinformation of the radio resource control for the D2UE connection 710may include information for radio resource which can be utilized by theD2UE connection 710 or may include information for radio resource whichcannot be utilized by the D2UE connection 710. The radio resource mayinclude at least one of time domain resource, frequency domain resource,and code domain resource. The information of the radio resource controlis also transmitted to the D2UE communication section 504.

Furthermore, the control signaling may include information of linkadaptation for the D2UE connection 710. More specifically, the linkadaptation may be one of power control and adaptive modulation andcoding. The information of the power control may include information onthe maximum transmission output power in the D2UE connection 710.

Furthermore, the control signaling may include measurement results forthe D2UE connection 710. More specifically, the BS2D communicationsection 502 may transmit measurement results, which are conducted by theD2UE communication section 504. The measurement results may includeradio link quality for UL in the D2UE connection 710. The radio linkquality may include at least one of path loss between the small-nodedevice 500 and the user equipment 100, received signal-to-interferenceratio (SIR) for UL, and the like. Furthermore, the measurement resultsmay include interference power for UL in the D2UE connection 710.

The D2UE communication section 504 communicates with the user equipment100 utilizing the D2UE connection 710.

More specifically, the D2UE communication section 504 manages the D2UEconnection 710 between the small-node device 500 and the user equipment100, i.e. the D2UE communication section 504establishes/configures/re-configures/re-establishes/releases the D2UEconnection 710 between the small-node device 500 and the user equipment100. The management of the D2UE connection 710 may be based on thecontrol signaling transmitted by the base station 200.

The D2UE communication section 504 may conduct a link adaptation for theD2UE connection 710, such as power control and adaptive modulation andcoding. The link adaptation may be conducted based on parameters whichare signaled from the base station 200.

The D2UE communication section 504 transmits data to the user equipment100 and receives data from the user equipment 100 utilizing the D2UEconnection 710 for offload purposes. As described above, data for someof the radio bearers may be transmitted in the D2UE connection 710.

Hereinafter, data transferred from the user equipment 100 to the server600 is called “uplink data” and data transferred from the server 600 tothe user equipment 100 is called “downlink data”.

The D2UE communication section 504 transmits the downlink data to theuser equipment 100 using the D2UE connection 710. The downlink data istransferred from the server 600 via the core network 400 and theBackhaul communication section 506.

The D2UE communication section 504 receives the uplink data from theuser equipment 100 using the D2UE connection 710. The uplink data istransferred to the server 600 via the Backhaul communication section 506and the core network 400.

The D2UE communication section 504 also conducts measurements for theD2UE connection 710. More specifically, the D2UE communication section504 make measurements of radio link quality for the D2UE connection 710between the small-node device 500 and the user equipment 100. The radiolink quality may be at least one of pilot signal received power, pathloss, signal-to-interference ratio (SIR), channel state information,channel quality indicator, received signal strength indicator for UL inthe D2UE connection 710. The radio link quality may be calculated by thepilot signal transmitted by the user equipment 100. The path loss is theone between the small-node device 500 and the user equipment 100. Themeasurements may include interference power level in the frequency band,in which the communications in the D2UE connection 710 operates.

The D2UE communication section 504 reports the measurement results tothe base station 200 via the BS2D communication section 502 and the BS2Dconnection 730.

The Backhaul communication section 506 is connected to the core network400 via a backhaul link. The backhaul link may be a wired connection ora wireless connection or a mixture of a wired connection and a wirelessconnection. The wireless connection may be a connection provided by WiFi(Wireless LAN) or cellular system.

The Backhaul communication section 506 transmits to the D2UEcommunication section 504 the downlink data, which is transferred viathe backhaul link from the core network 400. The Backhaul communicationsection 506 transmits the core network 400 the uplink data via thebackhaul link, which is transferred from the D2UE communication section504.

The user equipment 100 according to this embodiment will be describedwith reference to FIG. 12.

The user equipment 100 according to this embodiment has a BS2UEcommunication section 102 and D2UE communication section 104. The BS2UEcommunication section 102 and the D2UE communication section 104 areconnected to each other.

The BS2UE communication section 102 communicates with the base station200 utilizing the BS2UE connection 720. As described above, data forsome of the radio bearers are transmitted in the BS2UE connection 720.For example, according to one or more embodiments of the presentdisclosure, control signaling such as RRC signaling and NAS signalingand MAC layer signaling may be transmitted in the BS2UE connection 720.Furthermore, packets for Voice over IP (VoIP) may also be transmitted inthe BS2UE connection 720. Data for some other data bearers may also betransmitted in the BS2UE connection 720.

As described above, the BS2UE communication section 102 maytransmit/receive data for all radio bearers to/from the base station200, when the D2UE connection 710 is dropped or not available.

Furthermore, the BS2UE communication section 102 receives controlsignaling for the D2UE connection 710 from the base station 200, andtransmits control signaling for the D2UE connection 710 to the basestation 200. The control signaling includes signaling forestablishing/configuring/re-configuring/re-establishing/releasing theD2UE connection 710. Signaling for D2UE connection handover may also beincluded in the control signaling. The control signaling is transmittedto the D2UE communication section 104. The control signaling may be RRClayer signaling in LTE. Alternatively, the control signaling may be MAClayer signaling in LTE. Alternatively, some of the control signaling maybe RRC signaling and others may be MAC layer signaling.

The control signaling may include parameters for at least one ofphysical layer, MAC layer, RLC layer, PDCP layer, or RRC layer in theD2UE connection 710. The control signaling may include information forthe radio bearers in the D2UE connection 710.

Furthermore, the control signaling may include information of radioresource control for the D2UE connection 710. As described above, theinformation of the radio resource control for the D2UE connection 710may include information for radio resource which can be utilized by theD2UE connection 710 or may include information for radio resource whichcannot be utilized by the D2UE connection 710. The radio resource mayinclude at least one of time domain resource, frequency domain resource,and code domain resource. The information of the radio resource controlis also transmitted to the D2UE communication section 504.

Furthermore, the control signaling may include information of linkadaptation for the D2UE connection 710. More specifically, the linkadaptation may be one of power control and adaptive modulation andcoding. The information of the power control may include information onthe maximum transmission output power in the D2UE connection 710.

Furthermore, the control signaling may include measurement results forthe D2UE connection 710. More specifically, the BS2UE communicationsection 102 may transmit measurement results, which are conducted by theD2UE communication section 104. The measurement results include DL radiolink quality between small-node device and the user equipment 100. Thesmall-node device may be the serving small-node device or may be theneighbor small-node device. The serving small-node device corresponds tothe one which communicates with the user equipment 100 using the D2UEconnection 710. Details of the DL radio link quality will be describedbelow.

The D2UE communication section 104 communicates with the small-nodedevice 500 utilizing the D2UE connection 710.

More specifically, the D2UE communication section 104 manages the D2UEconnection 710 between the small-node device 500 and the user equipment100, i.e. the D2UE communication section 104establishes/configures/re-configures/re-establishes/releases the D2UEconnection 710 between the small-node device 500 and the user equipment100. The management of the D2UE connection 710 may be based on thecontrol signaling transmitted by the base station 200.

The D2UE communication section 104 may conduct a link adaptation for theD2UE connection 710, such as power control and adaptive modulation andcoding. The link adaptation may be conducted based on parameters whichare signaled from the base station 200.

The D2UE communication section 104 transmits data to the small-nodedevice 500 in UL and receives data from the small-node device 500 in DLutilizing the D2UE connection 710 for offload purposes. As describedabove, data for some of the radio bearers may be transmitted in the D2UEconnection 710.

That is, the D2UE communication section 104 receives the downlink datafrom the small-node device 500 using the D2UE connection 710. Thedownlink data is transferred from the server 600 via the core network400 and the small-node device 500. The D2UE communication section 104transmits the uplink data to the small-node device 500 using the D2UEconnection 710. The uplink data is transferred to the server 600 via thesmall-node device 500 and the core network 400.

The D2UE communication section 104 also conducts measurements for D2UEconnection. More specifically, the D2UE communication section 104 makemeasurements of the DL radio link quality for the serving small-nodedevice 500 or for the neighbor small-node device. The DL radio linkquality may be at least one of pilot signal received power, path loss,signal-to-interference ratio (SIR), channel state information, channelquality indicator, received signal strength indicator. The radio linkquality may be calculated by the pilot signal transmitted by the servingsmall-node device or the neighbor small-node device. The path loss isthe one between the user equipment 100 and the serving small-node deviceor the one between the user equipment 100 and the neighbor small-nodedevice.

The D2UE communication section 104 reports the measurement results tothe base station 200 via the BS2UE communication section 102 and theBS2UE connection 720.

The base station 200 according to this embodiment will be described withreference to FIG. 13.

The base station 200 according to this embodiment has a BS2UEcommunication section 201, a BS2D communication section 202, D2UEcommunication control section 204, and a Backhaul communication section206. The BS2UE communication section 201, the BS2D communication section202, the D2UE communication control section 204, and the Backhaulcommunication section 206 are connected to each other.

The BS2UE communication section 201 communicates with the user equipment100 utilizing the BS2UE connection 720. As described above, data forsome of the radio bearers are transmitted in the BS2UE connection 720.For example, according to one or more embodiments of the presentdisclosure, control signaling such as RRC signaling and NAS signalingand MAC layer signaling may be transmitted in the BS2UE connection 720.Furthermore, packets for Voice over IP (VoIP) may also be transmitted inthe BS2UE connection 720. Data for some other data bearers may also betransmitted in the BS2UE connection 720.

As described above, the BS2UE communication section 201 maytransmit/receive data for all radio bearers to/from the user equipment100, when the D2UE connection 710 is dropped or not available. Someparts of data, such as U-plane data, transmitted from the user equipment100 are transferred to the core network 400 via the BS2UE communicationsection 201 and the Backhaul communication section 206. Some parts ofdata, such as U-plane data, transmitted from the server 400 aretransferred to the user equipment 100 via the Backhaul communicationsection 206 and the BS2UE communication section 201.

Furthermore, the BS2UE communication section 201 receives controlsignaling for the D2UE connection 710 from the user equipment 100, andtransmits control signaling for the D2UE connection 710 to the userequipment 100. Description for the control signaling is the same as theone for the user equipment 100, and therefore is omitted here.

The BS2D communication section 202 communicates with the small-nodedevice 500 utilizing the BS2D connection 730. The BS2D communicationsection 202 receives control signaling for the D2UE connection 710 fromthe small-node device 500, and transmits control signaling for the D2UEconnection 710 to the small-node device 500. Description for the controlsignaling is the same as the one for the small-node device 500, andtherefore is omitted here.

The control signaling for the D2UE connection 710 is produced by theD2UE communication control section 204 as described below, and istransferred to the user equipment 100 via the Macro2UE communicationsection 201. The control signaling is transmitted also to the small-nodedevice 500 via the BS2D communication section 202.

The D2UE communication control section 204 conducts radio linkconnection control for the D2UE connection 710. The radio linkconnection control includes at least one ofestablishing/configuring/re-configuring/re-establishing/releasing theD2UE connection 710. The parameters for the radio link connectioncontrol are transmitted to the user equipment 100 via the Macro2UEcommunication section 201. The parameters for the radio link connectioncontrol are transmitted also to the small-node device 500 via the BS2Dcommunication section 202. The parameters may include at least one ofphysical layer, MAC layer parameters, RLC layer parameters, PDCP layerparameters, and RRC layer parameters. The parameters may include theinformation for the radio bearers. The radio link connection control maybe referred to as radio resource control.

More specifically, the D2UE communication control section 204 maydetermine that the D2UE connection 710 should be released, when the pathloss between the user equipment 100 and the small-node device 500 islarger than a threshold. That is, the D2UE communication control section204 may send control signaling to release the D2UE connection 710. TheD2UE communication control section 204 may conduct such determinationbased on the measurement reports which are transmitted by at least oneof the user equipment 100 and the small-node device 500. Morespecifically, at least one of the user equipment 100 and the small-nodedevice 500 may detect whether or not the path loss is larger than thethreshold and send the measurement reports in case that the path loss islarger than the threshold. The D2UE communication control section 204may send the control signaling to at least one of the user equipment 100and the small-node device 500, after it receives the measurementreports. In the above examples, DL transmission power or UL transmissionpower in the D2UE connection 710 may be utilized instead of the pathloss.

Furthermore, the D2UE communication control section 204 conducts controlfor handover of the D2UE connection between the user equipment 100 andthe small-node device 500.

More specifically, the D2UE communication control section 204 receivesthe measurement reports, which are transmitted by the user equipment100, and determines whether or not the user equipment 100 should handover to the neighbor small-node device, which is more closed to the userequipment 100 than the serving small-node device. Here, the servingsmall-node device means the one which currently has the D2UE connection710 with the user equipment 100.

Furthermore, the D2UE communication control section 204 may control theradio resource for the D2UE connection 710. More specifically, the D2UEcommunication control section 204 assigns the radio resource for theD2UE connection 710 so that it will not interfere D2UE connections inthe neighbor small-node device. More specifically, the D2UEcommunication control section 204 assigns the radio resource for theD2UE connection 710 so that it will not overlap with the one of otherD2UE connections in the neighbor small-node device. The radio resourceincludes at least one of time domain resource, frequency domainresource, and code domain resource.

The radio resource may be indicated to the user equipment 100 and thesmall-node device 500 by parts of the parameters for the radio resourcecontrol. The parameters may include at least one of ID of the frequencydomain resource, ID of identification of the time domain resource, andID of identification of the code domain resource.

The radio resource, which is assigned to the D2UE connection 710, may bedetermined based on the number of the user equipment in the cell wherethe small-node device 500 provides the radio communication service.Alternatively, the radio resource may be determined based oninterference power level in the frequency band, in which thecommunications in the D2UE connection 710 operates.

Furthermore, the D2UE communication control section 204 may control thelink adaptation for the D2UE connection 710. More specifically, the linkadaptation may be one of power control and adaptive modulation andcoding. The information of the power control may include information onthe maximum transmission output power for DL or UL in the D2UEconnection 710.

The control signaling, which is determined based on the above control inthe D2UE communication control section 204, is transmitted to the userequipment 100 via the BS2UE communication section 201. The controlsignaling is transmitted to the small-node device via the BS2Dcommunication section 202.

The Backhaul communication section 206 has a backhaul link which isconnected to the core network 400. The Backhaul communication section206 transmits to the BS2UE communication section 201 the downlink data,which is received from the core network 400, and transmits to the corenetwork 400 the uplink data, which is received from the BS2UEcommunication section 201.

Referring to FIGS. 14 and 14A, an operation of the mobile communicationsystem according to one or more embodiments of the present invention isdescribed.

As shown in FIG. 14, in the step S801, traffic data, which should betransferred between the user equipment 100 and the server 600, occurs.The traffic data may be transmitted both in downlink and in uplink.Alternatively, it may be transmitted only in downlink or only in uplink.More specifically, traffic data occurring may correspond tosending/receiving e-mails, browsing web sites, downloading files,uploading files and the like. Traffic data may be referred to as “data”.

In the step S802, LTE connection between the base station 200 and theuser equipment 100 (the BS2UE connection 720 in FIG. 2) is established.When it is triggered by the user equipment, the user equipment 100 mayinitiate the connection by random access procedures. When it istriggered by the server 600, the base station may send a paging messageto initiate the connection. Step S802 corresponds to Step A802 in FIG.14A.

In this embodiment, it is assumed that the BS2D connection 730 is alwaysconfigured between the base station 200 and the small-node device 500.

In some other embodiments, however, a connection between the basestation 200 and the small-node device 500 (the BS2D connection 730) isestablished in the step S802 or just after the step S802. Theestablishment may be triggered by the base station 200 using controlsignaling. Furthermore, the small-node device 500 may start transmittingpilot signals for the D2UE connection 710 after it is requested by thebase station 200 in the above establishment procedures. As a result, itmay not cause significant interference with other communications in thefrequency band when it does not transmit the pilot signals.

In the step S803, the user equipment 100 makes measurements for the D2UEconnection, as described below. That is, the user equipment 100 makesmeasurements for the DL radio link quality in the D2UE connection. Morespecifically, the user equipment 100 transmits to the base station 200 ameasurement report, which notifies the base station 200 ofidentification number of the small-node device having the best DL radiolink quality.

More specifically, the measurements for the D2UE connection may beconducted as illustrated in the steps A803 a, A803 b and A803 c in FIG.14A.

In the step A803 a, the base station 200 transmits control signaling tothe user equipment 100 in the BS2UE connection 720 and orders for theuser equipment 100 to make measurements for the D2UE connection so thatthe user equipment 100 detects small-node device with the best radiolink quality.

The control signaling may include information for the measurements. Forexample, according to one or more embodiments of the present disclosure,the control signaling may include at least one of carrier frequency forthe D2UE connection, bandwidth of the D2UE connection, identificationnumber for small-node device, information on measurement quantity,information on the pilot signals transmitted by the small-node deviceand the like. The information on the measurement quantity may be anindicator of RSRP or RSRQ.

The information on the pilot signals may be the one for the radioresource of the pilot signals. More specifically, it may be at least oneof the transmission periodicity of the pilot signals, thefrequency-domain resource information of the pilot signals, thetime-domain resource information of the pilot signals, and the like. Asmentioned later, time offset between the D2UE connection and the BS2UEconnection may also be included in the information on the pilot signals.Furthermore, transmission power of the pilot signals may be included inthe information on the pilot signals.

Furthermore, rules for sending measurement reports to the base station200 may also be included in the information for the measurements. Therules may include criteria, which are similar to the ones for LTE, suchas Event A1, A2, A3, A4, A5 and the like, which is specified in TS36.331. Threshold value or Layer-3 filtering coefficient,Time-to-trigger may also be included in the information for themeasurements.

Furthermore, control signaling for cell selection/reselection may alsobe included in the information for the measurements. That is, controlsignaling for idle-mode measurements may also be included in theinformation for the measurements.

The control signaling may be transmitted in the dedicated controlsignaling or in the broadcast information.

Furthermore, the control signaling in the step S803A may include anindicator whether or not the D2UE connection is available in the cellwherein the base station 200 provides the radio communication system forthe user equipment 100.

The control signaling may be transmitted in the step A802, instead ofthe step A803 a.

In the step A803 b, the user equipment 100 makes measurements for the DLradio link quality in the D2UE connection.

In the step A803 c, the user equipment 100 transmits to the base station200 a measurement report in the BS2UE connection 720, which notifies thebase station 200 of identification number of the small-node devicehaving the best DL radio link quality.

In the step S804, D2UE connection between the user equipment 100 and thesmall-node device 500 (the D2UE connection 710) is established. The basestation 200 orders for the user equipment 100 and the small-node device500 to configure the D2UE connection 710. The parameters for the D2UEconnection 710 are transmitted from the base station 200 to the userequipment 100 and the small-node device 500 in the BS2UE connection 720and in the BS2D connection 730, respectively. Furthermore, theestablishment of the D2UE connection 710 may be reported to the basestation 200 by the user equipment 100 and/or the small-node device 500.The step S804 corresponds to Steps A804 a to A804 f in FIG. 14A.

That is, the establishment of the D2UE connection 710 may be conductedas illustrated in the steps A804 a, A804 b, A804 c, A804 d, A804 e, andA804 f in FIG. 14A.

In the step A804 a, the base station 200 transmits control signaling tothe small-node device 500 in the BS2D connection 730 and orders thesmall-node device 500 to establish the D2UE connection 710 with the userequipment 100. In general, the small-node device 500 is the one whichhas the best DL radio link quality based on the measurement report. Inthe step A804 b, the small-node device 500 may transmit acknowledgementabout the order of the step A804 a. The control signaling may include atleast one of identification number of the user equipment 100, capabilityinformation of the user equipment 100, and the like.

In the step A804 c, the base station 200 transmits control signaling tothe user equipment 100 in the BS2UE connection 720 and orders the userequipment 100 to establish the D2UE connection 710 with the small-nodedevice 500.

For example, according to one or more embodiments of the presentdisclosure, the control signaling of the step A804 c may include atleast one of the following parameters:

Radio bearer information for the D2UE connection 710

Carrier frequency information of the D2UE connection 710

Frequency band indicator of the D2UE connection 710

System bandwidth (Channel bandwidth) of the D2UE connection 710

Cell barred information on the D2UE connection 710

Identification number of the small-node device 500

UL Maximum transmission power in the D2UE connection 710

Information of DL and UL slots in the D2UE connection 710 (in case ofTDD)

Information of random access channel for the D2UE connection 710

Information of uplink physical control channels, such as PUCCH for theD2UE connection 710

Information of downlink physical control channels, such as PDCCH, PHICHfor the D2UE connection 710

Information of uplink physical shared channel for the D2UE connection710

Information of downlink physical shared channel for the D2UE connection710

Information of uplink sounding reference signal for the D2UE connection710

Information of uplink power control information for the D2UE connection710

Information of downlink or uplink cyclic prefix information for the D2UEconnection 710

Information of time alignment control in uplink for the D2UE connection710

Information of RLC or PDCP configuration for each radio bearer for theD2UE connection 710

Information of MAC configuration for the D2UE connection 710

Information of security for the D2UE connection 710

Part or all of the information in the step A804 c may be transmitted tothe small-node device 500 in the step A804 a.

The radio bearer information may indicate what kind of radio bearersshould be configured for the D2UE connection 710 or what kind ofpriority should be specified for each radio bearer.

Because the parameters for the D2UE connection 710 can be transmitted inthe step A804 c, the small-node device 500 may neither have to transmitbroadcast channels, and therefore the complexity of the small-nodedevice 500 can be reduced.

In the step A804 d, the user equipment 100 transmits control signalingto establish a connection between the user equipment 100 and thesmall-node device 500 (the D2UE connection 710). The control signalingmay be a random access signaling. Alternatively, the control signalingmay be a pre-assigned access signaling. Radio resource information ofthe pre-assigned access signaling may be transmitted to the userequipment 100 by the base station 200 in the step A804 c.

The radio resource information of the pre-assigned access signaling maybe configured by the base station 200. In this case, the base station200 may notify the small-node device 500 of it in the step A804 a.Alternatively, the radio resource information of the pre-assigned accesssignaling may be configured by the small-node device 500. In this case,the small-node device 500 may notify the base station 200 of it in thestep A804 b.

In the step A804 e, the small-node device 500 transmits acknowledgementof the control signaling transmitted in the step A804 d. As a result,the D2UE connection 710 can be established.

In the step A804 f, the user equipment 100 transmits control signalingto the base station 200 and notifies the base station 200 that the D2UEconnection 710 has been successfully established.

In the step S805, some parts (Data #2 in FIG. 3) of the traffic data aretransferred between the user equipment 100 and the server 600 via theD2UE connection 710 and the small-node device 500, as described in FIG.3. The data transmitted in the D2UE connection 710 may be data for someparts of radio bearers, which are configured for the communicationbetween the user equipment 100 and the server 600. More specifically,the data transferred via the D2UE connection 710 may be at least one ofbest effort packets, non-real time service packets, and real timeservice packets. The data transferred via the D2UE connection 710 may beU-plane data. The step S805 corresponds to Step A805 in FIG. 14A.

In the step S806, some parts (Data #1 in FIG. 3) of the traffic data aretransferred between the user equipment 100 and the server 600 via theBS2UE connection 720 and the base station 200, as described in FIG. 3.C-plane data may also be transmitted in the BS2UE connection 720,instead of the D2UE connection 710. The step S806 corresponds to StepA806 in FIG. 14A.

The operations shown in FIG. 14 may be described in terms of theoperations in the small-node device 500 in the following. The operationsof the small-node device 500 comprise establishing the D2UE connection710 with the user equipment 100 (step S804) and transferring some partsof data, which are transferred between the user equipment 100 and theserver 600, using the D2UE connection 710 (step S805).

The operations shown in FIG. 14 may be described in terms of theoperations in the user equipment 100 in the following. The operations ofthe user equipment 100 comprise establishing the LTE connection (theBS2UE connection 720) with the base station 200 (step S802), makingmeasurements for the small-node device (step S803), establishing theD2UE connection 710 with the small-node device 500 (step S804),transferring some parts of data, which are transferred between the userequipment 100 and the server 600, via the D2UE connection 710 and thesmall-node device 500 (step S805), and transferring some parts of data,which are transferred between the user equipment 100 and the server 600,via the BS2UE connection 720 and the base station 200 (step S806).

The operations shown in FIG. 14 may be described in terms of theoperations in the base station 200 as follows. The operations of thebase station 200 comprise establishing the LTE connection (the BS2UEconnection 720) with the user equipment 100 (step S802), transmittingcontrol signaling for establishing the D2UE connection 710 (step S804),and transferring some parts of data, which are transferred between theuser equipment 100 and the server 600, using the BS2UE connection 720(step S806). In the D2UE connection 710, some parts of data, which aretransferred between the user equipment 100 and the server 600, aretransferred via the D2UE connection 710 and the small-node device 500.

Referring to FIG. 15, an operation of the mobile communication systemaccording to one or more embodiments of the present invention isdescribed.

As shown in FIG. 15, in the step S901, some parts of the traffic dataare transferred between the user equipment 100 and the server 600 viathe D2UE connection 710 and the small-node device 500. In the step S902,some parts of the traffic data are transferred between the userequipment 100 and the server 600 via the BS2UE connection 720 and thebase station 200. The steps S901 and S902 may be the same as the stepsS805 and S806, respectively, i.e. the steps S901 and S902 may be acontinuation of the steps S805 and S806.

In the step S903, traffic data, which should be transferred between theuser equipment 100 and the server 600, disappears. More specifically,traffic data disappearing may correspond to the end of sending/receivinge-mails, browsing web sites, downloading files, uploading files and thelike.

In the step S904, the base station 200 transmits control signaling tothe small-node device 500 and notifies the small-node device 500 thatthe D2UE connection 710 should be released. In the step S905, thesmall-node device 500 transmits acknowledgement of the notification ofthe step S904.

In the step S906, the base station 200 transmits control signaling tothe user equipment 100 and notifies the user equipment 100 that the D2UEconnection 710 should be released. In the step S907, the user equipment100 transmits acknowledgement of the notification of the step S906. Thesteps S906 and S907 may be conducted before the steps S904 and S905.Alternatively, the steps S906 and S907 may be conducted simultaneouslywith the steps S904 and S905.

According to the control signaling in the steps S904 and S906, the D2UEconnection 710 is released in the step S908.

The steps S905 and S907 may be conducted after the step S908 so that theuser equipment 100 or the small-node device 500 can report that the D2UEconnection 710 is released.

In the step S909, the base station 200 transmits control signaling tothe user equipment 100 and notifies the user equipment 100 that theBS2UE connection 720 is released. In the step S910, the user equipment100 transmits acknowledgement of the control signaling of the step S909to the base station 200. The steps S909 and S910 correspond to normalprocedures to release a LTE connection.

In the embodiment described in FIG. 15, the base station 200 transmitsthe control signaling to notify releasing the D2UE connection 710, butalternatively, the user equipment 100 or the small-node device 500 maytransmit the control signaling.

The operations shown in FIG. 15 may be described in terms of theoperations in the small-node device 500 in the following. The operationsof the small-node device 500 comprise transferring some parts of data,which are transferred between the user equipment 100 and the server 600,using the D2UE connection 710 (step S901), receiving the controlsignaling transmitted by the base station 200 (step S904), transmittingthe acknowledgement of the control signaling to the base station 200(step S905) and releasing the D2UE connection 710 with the userequipment 100 (step S908).

The operations shown in FIG. 15 may be described in terms of theoperations in the user equipment 100 in the following. The operations ofthe user equipment 100 comprise transferring some parts of data, whichare transferred between the user equipment 100 and the server 600, viathe D2UE connection 710 and the small-node device 500 (step S901),transferring some parts of data, which are transferred between the userequipment 100 and the server 600, via the BS2UE connection 720 and thebase station 200 (step S902), receiving the control signalingtransmitted by the base station 200 (step S906), transmitting theacknowledgement of the control signaling to the base station 200 (stepS907), releasing the D2UE connection 710 with the user equipment 100(step S908), and releasing the LTE connection (the BS2UE connection 720)in the steps S909 and S910.

The operations shown in FIG. 15 may be described in terms of theoperations in the base station 200 as follows. The operations of thebase station 200 comprise transmitting to the small-node device 500control signaling for releasing the D2UE connection 710 (step S904),transmitting to the user equipment 100 control signaling for releasingthe D2UE connection 710 (step S906), and releasing the BS2UE connection720 (steps S909 and S910).

Referring to FIG. 16, an operation of the mobile communication systemaccording to one or more the embodiments of the present invention isdescribed.

As shown in FIG. 16, in the step S1001, some parts of the traffic dataare transferred between the user equipment 100 and the server 600 viathe D2UE connection 710 and the small-node device 500. In the stepS1002, some parts of the traffic data are transferred between the userequipment 100 and the server 600 via the BS2UE connection 720 and thebase station 200. The steps S1001 and S1002 may be the same as the stepsS805 and S806, respectively, i.e. the steps S1001 and S1002 may be acontinuation of the steps S805 and S806.

In the step S1004, the base station 200 transmits control signaling tothe small-node device 500 and notifies the small-node device 500 thatthe D2UE connection 710 should be reconfigured. In the step S1005, thebase station 200 transmits control signaling to the user equipment 100and notifies the user equipment 100 that the D2UE connection 710 shouldbe reconfigured.

More specifically, the parameters described for the step A804 c may beincluded in the control signaling for the step 1004 or the step S1005.

In the step S1006, the D2UE connection 710 is re-configured. Morespecifically, some of the parameters for the D2UE connection 710 arechanged. The parameters may include at least one of parameters forfrequency domain resource, parameters for time domain resource,parameters for code domain resource, parameters for pilot signals forthe D2UE connection 710, parameters for initial access for the D2UEconnection 710, parameters for the radio bearers, parameters for thepower control for the D2UE connection 710. The parameters for the powercontrol include the information on the maximum transmission output powerfor DL or UL in the D2UE connection 710.

In the step S1007, the small-node device 500 transmits control signalingto the base station 200 and notifies the base station 200 that the D2UEconnection 710 has successfully been reconfigured. In the step S1008,the user equipment 100 transmits control signaling to the base station200 and notifies the base station 200 that the D2UE connection 710 hassuccessfully been reconfigured.

The operations shown in FIG. 16 may be described in terms of theoperations in the small-node device 500 in the following. The operationsof the small-node device 500 comprise transferring some parts of data,which are transferred between the user equipment 100 and the server 600,using the D2UE connection 710 (step S1001), receiving control signalingto reconfigure the D2UE connection 710 (step S1004), reconfiguring theD2UE connection 710 (step S1006), and transmitting control signaling toreport that the D2UE connection 710 has been reconfigured (step S1008).

The operations shown in FIG. 16 may be described in terms of theoperations in the user equipment 100 in the following. The operations ofthe user equipment 100 comprise transferring some parts of data, whichare transferred between the user equipment 100 and the server 600, usingthe D2UE connection 710 (step S1001), transferring some parts of data,which are transferred between the user equipment 100 and the server 600,using the BS2UE connection 720 (step S1002), receiving control signalingto reconfigure the D2UE connection 710 (step S1005), reconfiguring theD2UE connection 710 (step S1006), and transmitting control signaling toreport that the D2UE connection 710 has been reconfigured (step S1008).

The operations shown in FIG. 16 may be described in terms of theoperations in the base station 200 in the following. The operations ofthe base station 200 comprise transferring some parts of data, which aretransferred between the user equipment 100 and the server 600, using theBS2UE connection 720 (step S1002), transmitting to the small-node device500 control signaling to reconfigure the D2UE connection 710 (stepS1003), transmitting to the user equipment 100 control signaling toreconfigure the D2UE connection 710 (step S1004), receiving controlsignaling to report that the D2UE connection 710 has been reconfigured(step S1007), and receiving control signaling to report that the D2UEconnection 710 has been reconfigured (step S1008).

Referring to FIG. 17, an operation of the mobile communication systemaccording to one or more embodiments of the present invention isdescribed.

As shown in FIG. 17, in the step S1101, some parts of the traffic dataare transferred between the user equipment 100 and the server 600 viathe D2UE connection 710 and the source small-node device 500. In thestep S1102, some parts of the traffic data are transferred between theuser equipment 100 and the server 600 via the BS2UE connection 720 andthe base station 200. The steps S1101 and S1102 may be the same as thesteps S805 and S806, respectively, i.e. the steps S1101 and S1102 may bea continuation of the steps S805 and S806.

In the step S1103, the user equipment 100 makes measurements for theD2UE connection, as described below. That is, the user equipment 100makes measurements for the DL radio link quality of the servingsmall-node device and the neighbor small-node device. The DL radio linkquality may be at least one of pilot signal received power, path loss,signal-to-interference ratio (SIR), channel state information, channelquality indicator, received signal strength indicator, and the like.

More specifically, the user equipment 100 determines whether or not theneighbor small-node device, which is closer to the user equipment 100than the serving small-node device, is detected, and transmits to thebase station a measurement report if the neighbor small-node device isdetected, as illustrated in FIG. 17A.

That is, the user equipment 100 makes measurements for the D2UEconnection in the step A1103 a.

In the step A1103 b, the user equipment 100 determines whether or notthe neighbor small-node device, which is closer to the user equipment100 than the serving small-node device, is detected. The servingsmall-node device means the small-node device (the source small-nodedevice 500), which is currently communicating with the user equipment100. More specifically, the radio link quality of the neighborsmall-node device is higher than that of the serving small-node device,it may be determined that the neighbor small-node device is closer tothe user equipment 100 than the serving small-node device.

In a case where the neighbor small-node device, which is closer to theuser equipment than the serving small-node device, is detected (stepA1103 b: YES), the user equipment 100 transmits a measurement report tothe base station 200 so as to notify the base station that the neighborsmall-node device is detected. The step A1103 b corresponds to the stepS1104 in FIG. 17.

In a case where the neighbor small-node device, which is closer to theuser equipment than the serving small-node device, is not detected (stepA1103 b: NO), the user equipment 100 does not transmit the measurementreport to the base station 200.

The steps A1103 a and A1103 b correspond to the step S1103 in FIG. 17.

In the step S1104, the user equipment 100 transmits a measurement reportto the base station 200 so as to notify it that the neighbor small-nodedevice, which is closer to the user equipment than the servingsmall-node device, is detected.

Hereinafter, the serving small-node device is called “Source small-nodedevice” 500S and the neighbor small-node device is called “Targetsmall-node device” 500T.

The base station 200 makes a decision that the user equipment 100 shouldhandover to the neighbor small-node device (the target small-nodedevice) in the step S1105.

In the step S1106, the base station 200 transmits control signaling tothe target small-node device 500T for handover preparation. The controlsignaling may be called handover request for D2UE connection. Morespecifically, the base station 200 notifies it of parameters for thetarget small-node device to establish the D2UE connection with the userequipment 100. The parameters described in the step A804 a may beincluded in the ones in the control signaling of the step S1108.

In the step S1107, the target small-node device 500T transmitsacknowledgement of the control signaling of the step S1106.

In the step S1108, the base station 200 transmits control signaling tothe user equipment 100 and orders for the user equipment 100 to makehandover to the target small-node device 500T.

The control signaling may include connection information for the D2UEconnection 710. More specifically, the connection information mayinclude at least one of information on measurement configuration for theD2UE connection 710, information on mobility control for the D2UEconnection 710, radio resource control information for the D2UEconnection 710, and the like.

Furthermore, the radio resource control information for the D2UEconnection 710 may include at least one of radio bearer information forthe D2UE connection 710, information for PDCP layer configuration in theD2UE connection 710, information for RLC layer configuration in the D2UEconnection 710, information for MAC layer configuration in the D2UEconnection 710, information for physical layer configuration in the D2UEconnection 710, and the like.

More specifically, the parameters described for the step A804 c may beincluded in the radio resource control information for the D2UEconnection 710.

In the step S1109, the base station 200 transmits control signaling tothe source small-node device 500S and notifies it that the userequipment 100 should make handover to the target small-node device 500T.The source small-node device 500 ends the communications with the userequipment 100 based on the control signaling, i.e. the source small-nodedevice releases the D2UE connection 710.

In the step S1110, the user equipment 100 transmits control signaling toestablish a connection between the user equipment 100 and the targetsmall-node device 500T. The control signaling may be a random accesssignaling. The control signaling may be the same as the one in the stepA804 c.

In the step S1111, the target small-node device 500T transmitsacknowledgement of the control signaling transmitted in the step S1110.As a result, the D2UE connection can be established between the userequipment 100 and the target small-node device.

In the step S1112, the user equipment 100 transmits control signaling tothe base station 200 and notifies the base station 200 that the handoverto the target small-node device 500T has been successfully conducted.

In the steps S1113, some parts of the traffic data are transferredbetween the user equipment 100 and the server 600 via the D2UEconnection 710 and the target small-node device 500T.

In the step S1114, some parts of the traffic data are transferredbetween the user equipment 100 and the server 600 via the BS2UEconnection 720 and the base station 200. The step S1114 is the same asthe step S1102. That is, the step (S1102 and S1114) may be continuouslyconducted during the procedures described in FIG. 17.

The operations shown in FIG. 17 may be described in terms of theoperations in the source small-node device 500S as follows. Theoperations of the source small-node device 500S comprise transferringsome parts of data, which are transferred between the user equipment 100and the server 600, using the D2UE connection 710 (step S1101),receiving control signaling to notify the source small-node device 500Sthat the user equipment 100 should make handover to the targetsmall-node device 500T, and ending the D2UE connection 710 with the userequipment 100.

The operations shown in FIG. 17 may be described in terms of theoperations in the target source small-node device 500T in the following.The operations of the target small-node device 500T comprise receivingcontrol signaling for handover preparation, which is transmitted by thebase station 200 (step S1106), transmitting acknowledgement of thecontrol signaling (step S1107), receiving control signaling to establisha connection between the user equipment 100 and the target small-nodedevice 500 (step S1110), transmitting acknowledgement of the controlsignaling (step S1111), and transferring some parts of data, which aretransferred between the user equipment 100 and the server 600, using theD2UE connection 710 (step S1113).

The operations shown in FIG. 17 may be described in terms of theoperations in the user equipment 100 in the following. The operations ofthe user equipment 100 comprise transferring some parts of data, whichare transferred between the user equipment 100 and the server 600, usingthe D2UE connection 710 with the source small-node device (step S1101),transferring some parts of data, which are transferred between the userequipment 100 and the server 600, using the BS2UE connection 720 (stepS1102), making measurements for the D2UE connection (step S1103),transmitting a measurement report to the base station 200 (step S1104),receiving control signaling which orders the user equipment 100 to makethe handover to the target small-node device 500T (step S1108),transmitting control signaling to establish a connection between theuser equipment 100 and the target small-node device 500T (step S1110),transmitting control signaling to the base station 200 to notify thebase station 200 that the handover to the target small-node device 500Thas been successfully conducted (step S1112), receiving acknowledgementof the control signaling (step S1111), transferring some parts of data,which are transferred between the user equipment 100 and the server 600,using the D2UE connection 710 with the target small-node device 500T(step S1113), and transferring some parts of data, which are transferredbetween the user equipment 100 and the server 600, using the BS2UEconnection 720 (step S1114). It is noted that the step S1102 is the sameas the step S1114, and this procedure may be continuously conductedduring all the steps.

The operations shown in FIG. 17 may be described in terms of theoperations in the base station 200 in the following. The operations ofthe base station 200 comprise transferring some parts of data, which aretransferred between the user equipment 100 and the server 600, using theBS2UE connection 720 (step S1002), receiving a measurement reporttransmitted by the user equipment 100 (step S1104), making a decisionthat the user equipment 100 should handover to the target small-nodedevice 500T (step S1105), transmitting control signaling to the targetsmall-node device 500T for handover preparation (step S1106), receivingacknowledgement of the control signaling (step S1107), transmittingcontrol signaling to the user equipment 100 to order for the userequipment 100 to make the handover to the target small-node device 500T,transmitting control signaling to the source small-node device 500S tonotify it that the user equipment 100 should make the handover to thetarget small-node device 500T, receiving control signaling to notify thebase station 200 that the handover to the target small-node device 500Thas been successfully conducted (step S1112), and transferring someparts of data, which are transferred between the user equipment 100 andthe server 600, using the BS2UE connection 720 (step S1114).

Referring to FIG. 18, an operation of the base station 200 according toone or more embodiments of the present invention is described. Thecontrol method described in FIG. 18 is one example of the radio resourcecontrol or call admission control for the D2UE connection 710 in one ormore embodiments of the present invention.

In the step S1201, the base station 200 determines whether or not thenumber of the user equipment using the D2UE connection 710 is largerthan predetermined threshold.

Alternatively, the base station 200 may define congestion level, whichmay be determined based on at least one of the number of active userequipment, the number of the D2UE connections, amount of traffic data,interference level in the frequency band, where the D2UE communicationsoperate, and the like, and may determine whether or not the congestionlevel is higher than predetermined threshold. In other words, the basestation 200 may determine whether or not the congestion level is high inthe cell in the step S1201.

In a case where the number of the user equipment is not larger than thepredetermined threshold (step S1201: NO), the base station 200 allowsnewly configuring D2UE connection between the small-node device 500 andthe user equipment 100 in the step S1202. More specifically, when atraffic data occurs similarly to the step S801 and the user equipment100 tries to configure a new BS2UE connection with the base station 200and a new D2UE connection with the small-node device 500, the basestation 200 allows configuring the new D2UE connection with thesmall-node device 500, in addition to the new BS2UE connection with thebase station 200. Alternatively, when the user equipment 100 tries toconfigure a new D2UE connection with the small-node device in a statewherein the user equipment 100 has a BS2UE connection with the basestation 200, the base station 200 may allow the new D2UE connection withthe small-node device 500.

In a case where the number of the user equipment is larger than thepredetermined threshold (step S1201: YES), the base station 200 does notallow newly configuring D2UE connection between the small-node device500 and the user equipment 100 in the step S1203. More specifically,when a traffic data occurs similarly to the step S801 and the userequipment 100 tries to configure a new BS2UE connection with the basestation 200 and a new D2UE connection with the small-node device 500,the base station 200 does not allow configuring the new D2UE connectionwith the small-node device 500. Here, the base station 200 may allowconfiguring the new BS2UE connection with the base station 200, but maynot allow only the new D2UE connection with the small-node device 500.Alternatively, when the user equipment 100 tries to configure a new D2UEconnection with the small-node device in a state wherein the userequipment 100 has a BS2UE connection with the base station 200, the basestation 200 may not allow the new D2UE connection with the small-nodedevice 500.

In the above examples, the small-node device 500 has one D2UE connectionwith one user equipment 100, but it may have more than one D2UEconnections with more than one user equipment, similarly to normal basestation. The radio resource for each D2UE connection may be shared bythe multiple user equipment and may be controlled by the base station200 or the small-node device 500.

In the above examples, D2UE (the D2UE connection 710) and BS2UE (theBS2UE connection 720) transmissions can operate in different frequencybands, but in other embodiments D2UE may operate concurrently in thesame frequency band as the Macro system (BS2UE). In this scenario, someinterference mitigation techniques may be utilized in order to achieveco-existence between D2UE and BS2UE in the same frequency band.

For example, according to one or more embodiments of the presentdisclosure, because the base station 200 configures the D2UE connection710, the base station 200 is aware that the user equipment 100 will notrespond to signaling by the base-station in various frequency/timeslots. In some such embodiments the D2UE connection 710 is configured soas to allow transmission slots where BS2UE (the base station 200 to theuser equipment 100) communications can be made in order to supportcontinued connection and management by the base station 200. In otherwords, the user equipment 100 can communicate with the base station 200in predetermined on-duration, and the user equipment 100 can communicatewith the small-node device 500 in the other duration (off-duration).

Alternatively, in other embodiments where the D2UE connection 710 insupport of the small-node device 500 to the user equipment 100communication link occur concurrently in the same band as withtransmission of the base station 200, OFDM Resource Elements (RE) invarious resource blocks (RBs) are reserved for each link. In oneembodiment REs used for control signaling are not used by the D2UE linkand thus are left blank in any D2UE link transmission. D2UE linktransmissions, including its own control signaling to the user equipment100, are sent in other REs. In such an embodiment the user equipment 100is in fact able to receive REs, e.g. control REs, from the base station200 concurrently with communication from the small-node device 500. Thebase station may turn off transmissions or reduce transmission power inthe BS2UE link in the radio resource, in which transmissions in the D2UElink may occur. The radio resource may be time domain resource orfrequency domain resource.

In at least one of the above embodiments, the D2UE link may be similarto normal BS2UE link, i.e. the small-node device 500 may transmit commonpilot signals, broadcast signals, synchronization signals, physicallayer control signaling and the like. Alternatively, some parts of thesignals and channels may be transmitted and others may not betransmitted in the D2UE link. For example, according to one or moreembodiments of the present disclosure, common pilot signals and physicallayer control signaling may be transmitted in the D2UE link, and otherchannels and signals, such as broadcast channels/signals,synchronization signals and the like, may not be transmitted in the D2UElink. Alternatively, common pilot signals may be transmitted in the D2UElink, and other channels and signals, such as physical layer controlsignaling, broadcast channels/signals, synchronization signals and thelike, may not be transmitted in the D2UE link. Alternatively, onlyinfrequently-transmitted pilot or synchronization signals may betransmitted in the D2UE link, and other channels and signals, such ascommon pilot signals, physical layer control signaling, broadcastchannels/signals, conventional synchronization signals and the like, maynot be transmitted in the D2UE link.

Alternatively, the D2UE link may be a device-to-device (D2D) link. Insuch a scenario, most of the common signals/channels, such as commonpilot signals, broadcast signals, synchronization signals, physicallayer control signaling and the like, can be omitted in the D2UE link,and only channels transferring data may be transmitted in the D2UE link.Alternatively, some of channels/signals, such asinfrequently-transmitted pilot or synchronization signals and physicallayer control signaling and the like, may be transmitted in the D2UElink even in this scenario.

Irrespective of whether the D2UE link is similar to the normal BS2UElink or to the D2D link, the D2UE link may be based on LTE-based radiointerface, or may be based on other radio system-based interface. Forexample, according to one or more embodiments of the present disclosure,the D2UE link may be based on WCDMA or CDMA2000 or WiFi or WiMAX or LTEadvanced or TD-SCDMA or TD-LTE.

For example, according to one or more embodiments of the presentdisclosure, the D2UE connection 710 may be specified based on aWiFi-based radio interface. In this example, a WiFi access point may beregarded as the small-node device 500. That is, the D2UE communicationsection 504 in the small-node device 500 communicates with the userequipment 100 utilizing the WiFi radio interface, and the radio resourcecontrol of the WiFi radio interface may be controlled by the basestation 200. The control signaling for the radio resource control may betransmitted in the BS2UE connection 720 and the BS2D connection 730.

Characteristics mentioned above may be described as follows. One of thecharacteristics in one or more embodiments of the present invention is amobile station in a mobile communication system, in which a mobilestation communicates with a server, and the mobile station comprises a1st communication unit configured to communicate with the radio basestation, a 2nd communication unit configured to communicate with adevice. The 1st communication unit is configured to transfer some partsof data, which are transferred between the mobile station and theserver, via the radio base station, and the 2nd communication unit isconfigured to transfer parts of data, which are transferred between themobile station and the server, via the device.

In the above mentioned mobile station, the 1st communication unit isconfigured to receive and transmit control signals from and to the radiobase station, which control the communication with the device.

In the above mentioned device, the 2nd communication unit is configuredto communicate with the device based on parameters signaled by the radiobase station. Here, the parameters may indicate time domain resource forthe communication with the device.

In the above mentioned mobile station, the 2nd communication unit isconfigured to offload the data, which is transferred between the mobilestation and the server, via the device.

In the above mentioned device, a 1st frequency for communicating withthe radio base station is different from a 2nd frequency forcommunicating with the device.

In the above mentioned device, the 1st communication unit and the 2ndcommunication unit are configured to conduct communicationssimultaneously utilizing functions with which the mobile station cantransmit/receive signals in different frequency bands simultaneously.

In the above mentioned device, the 1st communication unit and the 2ndcommunication unit are configured to conduct communicationssimultaneously in time division multiplexed manner.

One of the characteristics in one or more embodiments of the presentinvention is a device in a mobile communication system, in which amobile station communicates with a server via a radio base station orthe device, and the device comprises a 1st communication unit configuredto communicate with the radio base station, a 2nd communication unitconfigured to communicate with the mobile station, and a backhaul unitconfigured to communicate with the server. The 1st communication unitmay be configured to receive and transmit control signals from and tothe radio base station, which control the communication between themobile station and the device. The 2nd communication unit is configuredto receive some of data which is transferred from the mobile station tothe server, and the backhaul unit is configured to transmit it to theserver, and the backhaul unit is configured to receive data which istransferred from the server to the mobile station, and the 2ndcommunication unit is configured to transmit it to the mobile station.

In the above mentioned device, the 2nd communication unit and thebackhaul unit are configured to offload the data, which is transferredbetween the mobile station and the server.

One of the characteristics in one or more embodiments of the presentinvention is a radio base station in a mobile communication system, inwhich a mobile station communicates with a server, and the radio basestation comprises a 1st communication unit configured to communicatewith the mobile station, a 2nd communication unit configured tocommunicate with a device, and a control unit configured to control thecommunication between the mobile station and the device. Parts of data,which is transferred between the mobile station and the server, aretransferred via the device.

In the above mentioned radio base station, the 1st communication unit isconfigured to receive and transmit control signals from and to themobile station, which control the communication between the mobilestation and the device.

In the above mentioned radio base station, the 2nd communication unit isconfigured to receive and transmit control signals from and to thedevice, which control the communication between the mobile station andthe device.

In the above mentioned radio base station, the device is configured tooffload the data, which is transferred between the mobile station andthe server.

One of the characteristics in one or more embodiments of the presentinvention is a communication method of a mobile station in a mobilecommunication system, in which a mobile station communicates with aserver, the method comprising the steps:

(step B1) Communicating with the radio base station

(step B2) Communicating with a device

In step B2, parts of data, which is transferred between the server andthe mobile station, are transferred via the device.

One of the characteristics in one or more embodiments of the presentinvention is a communication method of a device in a mobilecommunication system, in which a mobile station communicates with aserver, the method comprising the steps:

(step A1) Communicating with the radio base station

(step A2) Communicating with the mobile station

(step A3) Communicating with the server

In step A1, control signaling for the communication with the mobilestation is transmitted. In the step A2 and A3, parts of data, which istransferred between the server and the mobile station, are transferredvia the device.

One of the characteristics in one or more embodiments of the presentinvention is a communication method of a radio base station in a mobilecommunication system, in which a mobile station communicates with aserver via a radio base station, the method comprising the steps:

(step C1) Communicating with the mobile station

(step C2) Communicating with a device

(step C3) Controlling the communication between the mobile station andthe device, and in step C1/C2/C3 parts of data, which is transferredbetween the server and the mobile station, are transferred via thedevice.

Some more embodiments for mobility procedures and radio resourcemanagements of the invention, such as cell identification, measurements,handover, cell selection/reselection, changing transport formats, calladmission control, radio resource control, link adaptation control,power control, releasing connections and the like, are explained in thefollowing. The following procedures are more detailed examples for theabove mentioned RRC connection state control for the D2UE connection710.

In mobile communication systems, mobility procedures, such as cellidentification, measurements, handover, cell selection/reselection andthe like, are quite important, because mobile communication connectivityshould be maintained even when a mobile station (user equipment) movesfrom one cell to other cells. Here it should be noted that if the mobilestation tries to detect neighbor cells and make measurements for thedetected neighbor cells very frequently, the connectivity is improved,but battery consumption of the mobile station increases, which degradesservice quality in the mobile communication system. That is, the mobilestation has to minimize the battery consumptions due to the mobilityprocedures, simultaneously with achieving good quality mobilityperformance.

Furthermore, the mobility procedures are quite important also in termsof interference in the mobile communication systems. That is, it is alsoquite important that the mobile station communicate with a base stationwith the highest radio link quality. The radio link quality isequivalent to at least one of path loss, pilot signal received power,signal-to-interference ration and the like. If the mobile station doesnot communicate with the base station with the highest link quality,i.e. it communicates with the second highest quality base station, itmay interfere with other communications because its transmit power maybe too high for other radio links, as illustrate d in FIG. 19.

In FIG. 19 (a), the mobile station #A1 communicates with the basestation with the second highest radio link quality, instead of the basestation with the highest radio link quality. As a result, signalstransmitted by the mobile station #A1 may interfere with thecommunication between the base station with the highest radio linkquality and other mobile stations. In FIG. 19 (b), however, the mobilestation #A1 communicates with the base station with the highest radiolink quality, and therefore the signals transmitted by the mobilestation #A1 may not interfere with other communications.

The interference may be intra-frequency interference, or may beinter-frequency interference. In the inter-frequency interference case,adjacent channel interference in the transmitter side or receiverblocking characteristics in the receiver side may degrade the quality inother communications.

The interference issues may be handled by not only the mobilityprocedures, but also other radio resource management procedures.

In short, the mobility procedures and other radio resource managementprocedures should be appropriately conducted in the mobile communicationsystems in order to achieve good quality connectivity, long battery lifein the mobile stations, less interference in the systems and the like.

In the above mentioned hybrid D2UE and BS2UE system, such mobilityprocedures and radio resource management procedures are conducted in theD2UE link, in addition to the Macro2UE link. It is noted that becausethe cell size in the D2UE link is small, mobility performance can bemore easily degraded and interference issues can happen more frequently.Therefore, the above mobility procedures and other radio resourcemanagement procedures are quite important for the D2UE link. Moredetails of the mobility procedures and other radio resource managementprocedures in the D2UE link are explained below:

In the following examples, it is assumed that the carrier frequency inthe D2UE connection 710 is 3.5 GHz, and the one in the BS2UE connectionbetween the base station 200 and the user equipment 100 is 2 GHz,similarly to the above examples. It is noted that the frequency bandsare just examples, and other frequency bands can be applicable in otherembodiments.

FIG. 20 illustrates the radio communication system according to at leastone embodiment. It is basically the same as FIG. 1, but is slightlymodified compared to FIG. 1 so that the mobility procedures and radioresource managements for the radio communication system can beillustrated. In FIG. 20, three small-node devices (500A, 500B, 500C) areshown for illustrative purpose.

Referring to FIG. 21, an operation of the mobile communication systemaccording to one or more embodiments of the present invention isdescribed. The operation is related to connection establishment in theD2UE connection 710. The operation may correspond to details of stepsS803 and S804 in FIG. 14 or steps A803 a, A803 b, A803 c, A804 a, A804b, A804 c, A804 d, A804 e, and A804 f in FIG. 14A.

In the step S1301, the base station 200 transmits control signaling forthe D2UE connection 710 to the user equipment 100. The control signalingmay be transmitted in the step A803 a in FIG. 14A, instead of the stepS1301. Alternatively, the control signaling may be transmitted as partsof broadcast information to the user equipment 100.

The control signaling may include at least one of information onfrequency resource for D2UE pilot signals, information on time resourcefor the D2UE pilot signals, information on code resource for the D2UEpilot signals. Some examples for the D2UE pilot signals are explainedlater.

The control signaling may include information on transmission power forthe D2UE pilot signals. That is, the transmission power for the D2UEpilot signals may be transmitted as one information element of thecontrol signaling. Furthermore, the control signaling may includeinformation on measurement behaviors in the user equipment 100.

In the step S1302, the small-node device 500 transmits the D2UE pilotsignals in predetermined radio resources. More specifically, thesmall-node device 500A, 500B, 500C transmits the D2UE pilot signals inthe predetermined radio resources. The radio resources may consist of atleast one of time resource, code resource and frequency resource. Theinformation on the predetermined radio resources may be signaled by thecontrol signaling described in the step S1301. In this sense,“predetermined radio resources” correspond to the radio resourceindicated by the base station 200.

More details of the D2UE pilot signals are explained below:

FIG. 22 illustrates one example of the radio resources for the D2UEpilot signals. In FIG. 22, the frequency resource #3 is assigned asfrequency radio resource, and the time resource #6 is assigned as timeradio resource. Furthermore, one code resource is assigned to onesmall-node device. For example, according to one or more embodiments ofthe present disclosure, the code resource #0, #1, and #2 may be assignedto the small-node device 500A, 500B, and 500C, respectively. The coderesource may be combination of the CAZAC sequence (or Zadoff-Chusequence) and cyclic shift, as shown below.

It is assumed that time synchronization is achieved for all the D2UEconnections, i.e. time slots for all the D2UE connections are alignedwith each other.

For the small-node device 500, the time synchronization may be achievedby GPS of each small-node device. Alternatively, the timesynchronization may be achieved by the BS2D connections, that is, thetime frame timing of the D2UE connections are based on the signalstransmitted by the base station 200, and therefore the time frame timingof the D2UE connections are aligned with each other. Other timesynchronization technique may be utilized in order to achieve the timesynchronization for the D2UE connections. In any case, the time frametiming of the D2UE connections is specified so that the time frametiming of the D2UE connections should be time-synchronized with eachother.

For the user equipment 100, the time synchronization may be achieved bythe BS2UE connection 720, that is, the time frame timing of the D2UEconnections are based on the signals transmitted by the base station200, and therefore the time frame timing of the D2UE connections isaligned with each other. Other time synchronization technique may beutilized in order to achieve the time synchronization for the D2UEconnections.

As a result, the time frame timing of the D2UE connections aretime-synchronized with each other for both the small-node device 500 andthe user equipment 100.

Time synchronization will be explained further below. For example,according to one or more embodiments of the present disclosure, asillustrated in FIG. 22A, the time slots for the D2UE connections may becompletely aligned with those for the BS2UE connections. Alternatively,as illustrated in FIG. 22B, there may be a time offset between the timeslots for the D2UE connections and the ones for the BS2UE connections.

More specifically, as illustrated in FIGS. 22C and 22D, each time offsetbetween the time slots for the D2UE connections and the ones for theBS2UE connections may be respectively specified for each macro (basestation) coverage area, which corresponds to the area supported by eachbase station 200. FIG. 22C illustrates explanatory views showing twomacro (base station) coverage areas, where some small-node devices aredeployed. FIG. 22D illustrates explanatory views showing time relationof BSUE connections and D2UE connections. In FIG. 22D, time offset #A isspecified for the macro (base station) #A coverage area, and time offset#B is specified for the macro (base station) #B coverage area. Each timeoffset can be specified so that all D2UE connections can be aligned witheach other in terms of time. The base station 200 may inform the userequipment 100 of the time offset value (time offset #A or time offset #Bin FIG. 22D) as part of control signaling. Furthermore, the base station200 may inform the small-node device 500 of the time offset value (timeoffset #A or time offset #B in FIG. 22D) as part of control signaling.The time offset value may be included in the control signaling in thestep S1301. As a result, even if there is no time synchronization forthe macro (base station) network, i.e. Macro #A is not aligned withMacro #B in terms of time, D2UE connections in the macro #A coveragearea can be aligned with those in the macro #B coverage area, asillustrated in FIG. 22D.

From a viewpoint of a receiver of the user equipment 100, the userequipment 100 has only to decode the D2UE pilot signals transmitted bymultiple small-node devices only in the predetermined radio resource(the frequency resource #3 and the time resource #6), and thereforepower consumptions for decoding the D2UE pilot signals can be minimized.More detailed examples, according to one or more embodiments of thepresent disclosure, are shown below. That is, the user equipment 100does not have to achieve time synchronization with multiple small-nodedevices because it has already been achieved by the time synchronizationwith the BS2UE connections, as mentioned above. It can reduce complexityfor the cell identification and as a result reduce the power consumptionfor the cell identification.

UE behavior for receiving the D2UE pilot signals are further explainedbelow:

As illustrated in FIG. 22E, the small-node devices 500A, 500B, 500C and500D transmit the D2UE pilot signals to the user equipment 100. Asmentioned above, one time and frequency domain resource may be used forall the D2UE pilot signals and different code may be assigned to eachpilot signal. For example, according to one or more embodiments of thepresent disclosure, the code resource #0, #1, #2, and #3 may be assignedto the small-node devices 500A, 500B, 500C and 500D, respectively.

Here, the CAZAC (Constant Amplitude Zero AutoCorrelation) sequence maybe used for the code. Additionally, the Zadoff-Chu sequence may be usedfor the code. Alternatively, the Walsh sequence may be used for thecode.

More specifically, the pilot signal may have a physical layer format asillustrated in FIG. 22F. That is, it may consist of cyclic prefix, asequence part, and a guard period. The guard period may be the same asblank. The above CAZAC sequence may apply to the sequence part.

In this scenario, the user equipment 100 may have a receiving window asillustrated in FIG. 22G, and has only to decode the D2UE pilot signalstransmitted by several small-node devices once. The user equipment 100may obtain delay profiles for each D2UE pilot signal as illustrated inFIG. 22H. The delay profiles for each D2UE pilot signal may be shifteddue to the cyclic shift of the Zadoff-Chu sequence, as illustrated inFIG. 22H. It is noted that the cyclic shift for the small-node device500A is assumed to zero in the figure. As a result, the user equipment100 can easily make measurements for delay and received power level ofthe D2UE pilot signal for each small-node device. As a result, UEcomplexity for cell search and measurements can be reduced.

The cyclic shift may be adjusted based on cell range of the small-nodedevice 500. Alternatively, the cyclic shift may be adjusted based oncell range of the base station 200. In case the cell range is large,time difference among the D2UE pilot signals is large and therefore thecyclic shift may be set to large. On the other hand, in case the cellrange is small, time difference among the D2UE pilot signals is smalland therefore the cyclic shift may be set to small. The base station 200may notify the user equipment 100 of the information of the cyclic shiftfor each small-node device using control signaling. More specifically,the information of the cyclic shift may be included in the controlsignaling in the step S1301. The base station 200 may notify thesmall-node device 500 of the information of the cyclic shift for thesmall-node device 500.

Physical random access channel (PRACH) or physical channel similar toPRACH may be used for the D2UE pilot signals. PRACH is defined as a LTEphysical channel in TS 36.211. That is, the small-node device 500transmits signals similar to a random-access-preamble in thepredetermined radio resource. The random access preamble may be assigneddedicatedly to the small-node device 500 by the base station 200. Thatis, the radio resource for the signals may be assigned by the basestation 200.

The D2UE pilot signals may be transmitted infrequently, as describedabove. For example, according to one or more embodiments of the presentdisclosure, the D2UE pilot signals may be transmitted once per 1 second.Because time synchronization is achieved by utilizing the BS2UEconnections, the D2UE pilot signals do not have to be transmittedfrequently. As a result, the user equipment 100 has only to decode theD2UE pilot signals once per 1 second, and the power consumptions for themeasurements can be minimized. Furthermore, the D2UE pilot signals aretransmitted much less frequently than the common reference signals orthe synchronization signals in LTE, and therefore interference caused bythe D2UE pilot signals can be minimized. The periodicity of the D2UEpilot signals may be very large, e.g. 1 second or 2 seconds, or may bereasonably large, e.g. 100 milliseconds or 200 milliseconds. In casethat the periodicity is very large, the power consumption formeasurements and the interference issues can be reduced significantly,but the user equipment 100 may need more time to detect neighborsmall-node devices and make measurements for them because it needs somemeasurement samples to achieve good accuracy. As a result, latency ofmobility procedures may be increased. In case that the periodicity isreasonably large, the power consumption for measurements andinterference issues may be reduced to some extent, but the latency willbe decreased. So, the periodicity of the D2UE pilot signals can beoptimized based on the above aspects, such as power consumption formeasurements, interference issues, latency of mobility procedures andthe like. The periodicity of the D2UE pilot signals may be networkconfigurable and the base station 200 may inform the user equipment 100of the periodicity by utilizing control signal. It may be included inthe control signaling in the step S1301. The base station 200 may informthe small-node device 500 of the periodicity by utilizing controlsignal.

In case that the user equipment 100 does not support multiple radiofrequency components which support simultaneous transmission/receptionfor a frequency carrier for the BS2UE connection 720 and a frequencycarrier for the D2UE connection 710, the user equipment 100 may stoptransmitting/receiving signals in the BS2UE connection 720 during thetime when the D2UE pilot signals are transmitted, so that it can makemeasurements for the D2UE connection 710. In this case, the base station200 may consider such behaviors of the user equipment 100 in itsscheduling for the BS2UE connection 720, i.e. the base station 200 mayavoid assigning radio resource to the user equipment 100 during timewhen the D2UE pilot signals are transmitted.

The D2UE pilot signal may be called D2UE sounding reference signal orD2UE synchronization signal.

The D2UE pilot signal may be mapped distributed in the frequency domainso that signal strength fluctuation due to Rayleigh fading may besuppressed and more accurate measurements for the radio link quality maybe achieved.

The base station 200 may notify the user equipment 100 of information onthe D2UE pilot signal for each small-node device. The information may beincluded in the control signaling in the step S1301. Some examples, someof which are shown above, of the information are listed below:

Code domain resource for the D2UE pilot signal

For example, index of the Zadoff-Chu sequence

Frequency domain resource for the D2UE pilot signal

Time domain resource for the D2UE pilot signal

Time offset between the D2UE connection and the BS2UE connection

Transmission power of the D2UE pilot signal

Cyclic shift information of the D2UE pilot signal

The above information is specified for each small-node device, andtherefore may be included in the neighbor cell list for the small-nodedevice. The above info nation may be signaled by broadcast informationin the BS2UE connection or by dedicated signaling in the BS2UEconnection.

In the above examples, according to one or more embodiments of thepresent disclosure, one time domain resource and frequency domainresource are specified as illustrated in FIG. 22. But, more than onetime domain resource or frequency domain resource may be configured forthe small-node device 500. Especially, in case that there are manysmall-node devices, the number of code-domain resource may not besufficient and more than one time domain resource or frequency domainresource may be used.

In the step S1303, the user equipment 100 receives the D2UE pilotsignals and makes measurements for the D2UE pilot signals in thepredetermined radio resources. That is, the user equipment 100 decodesthe D2UE pilot signals transmitted by multiple small-node devices 500and make measurements for the multiple small-node devices. Morespecifically, the user equipment 100 obtains radio link quality of D2UEconnections between itself and the multiple small-node devices. Theradio link quality may be at least one of path loss, received power ofthe D2UE pilot signal, SIR of the D2UE pilot signal, received quality ofthe D2UE pilot signal and the like. The user equipment 100 may detectthe small-node device which has the highest radio link quality based onthe measurements.

The path loss may be derived from the received power of the D2UE pilotsignals and the transmission power of the D2UE pilot signals, which areincluded in the control signaling in the step S1301. The receivedquality of the D2UE pilot signal may be the ratio of the receive powerof the D2UE pilot signal to total received signal strength.

In the step S1304, the user equipment 100 transmits measurement reportsto the base station 200. The measurement reports include the measurementresults obtained in the step S1303.

More specifically, the measurement reports may include the informationon the small-node device with the highest radio link quality. In otherwords, the user equipment 100 may report the best small-node device interms of the radio link quality of D2UE connections in the step S1304.The information on the small-node device may include the identificationnumber of the small-node device and the radio link quality of thesmall-node device.

Furthermore, the measurement report may include information on thesmall-node device with not-the-highest radio link quality, i.e. themeasurement report may include information on the small-node device withthe second or third highest radio link quality. The second or third maybe an example, and the fourth or more may be included. It may besignaled by the base station 200 in the step S1301 for how manysmall-node devices the information should be included in the measurementreport.

Alternatively the measurement reports may include the small-node device,for which the radio link quality is higher than a threshold. Thethreshold may be informed the user equipment 100 of by the base station200 in the step S1301.

Alternatively the measurement reports may include the small-node device,for which the radio link quality is lower than a threshold. Thethreshold may be informed the user equipment 100 of by the base station200 in the step S1301.

In the step S1305, the base station 200 establishes the D2UE connection710. More specifically, the base station 200 establishes the radio linkbetween the user equipment 100 and the small-node device with thehighest radio link quality, which is reported in the step S1304.

In the step S1305, the base station 200 may assign the radio resource tothe D2UE connection 710, in addition to establishing the radio resource.The radio resource may be at least one of the frequency domain resource,time domain resource, code domain resource, and the like. Morespecifically, the radio resource may be a carrier frequency for the D2UEconnection 710. For example, according to one or more embodiments of thepresent disclosure, the base station 200 may select the radio resource,which is not used by the small-node device with the second or thirdhighest radio link quality, which is reported in the step S1304. As aresult, it can be avoided that the D2UE connection, which is establishin the step S1305, cause interference with other D2UE connections in theneighbor small-node devices. Alternatively, the base station 200 mayassign the radio resource, which is not used by other small-node device500, which is located near the small-node device with the highest radiolink quality. The base station may have location information for thesmall-node device 500.

According to one or more embodiments as illustrated in FIG. 21, lowerpower consumptions for the measurements can be achieved. Furthermore,interference mitigation can also be realized.

Referring to FIG. 23, an operation of the mobile communication systemaccording to one or more embodiments of the present invention isdescribed. The operation is related to connection establishment in theD2UE connection 710. The operation may correspond to details of stepS804 in FIG. 14 or steps A803 a, A803 b, A803 c, A804 a, A804 b, A804 c,A804 d, A804 e, and A804 f in FIG. 14A.

Because the steps S1401 to S1404 are the same as the steps S1301 toS1304 in FIG. 21, explanation of the steps S1401 to S1404 is omitted.

In the step S1405, the base station 200 determines whether or not pathloss is lower than a threshold. More specifically, the base station 200determines whether or not the path loss for the small-node device withthe highest radio link quality is lower than the threshold.

In a case where the path loss for the small-node device with the highestradio link quality is lower than the threshold (Step S1405: YES), thebase station 200 establishes the D2UE connection 710 in the step S1406.In the step S1406, the base station 200 may assign the radio resource tothe D2UE connection 710, in addition to establishing the radio resource,similarly to the step S1305.

In a case where the path loss for the base station with the highestradio link quality is not lower than the threshold (Step S1405: NO), thebase station 200 does not establish the D2UE connection 710 in the stepS1407. That is, the base station 200 does not order for the userequipment 100 and the small-node device 500 to establish the D2UEconnection 710, and as a result the user equipment 100 communicates withthe server 600 only in the BS2UE connection 720.

Because the path loss is high and required transmission power is high,the D2UE connection may interfere with other D2UE connections orcommunications. Such interference issues can be mitigated by utilizingthe control illustrated in FIG. 23.

In the step S1405, path loss is used for the determination, but otherradio link quality, such as the received power of the D2UE pilot signal,the received quality of the D2UE pilot signal, the SIR of the D2UE pilotsignal and the like. In this case, in case that the radio link qualityis better than a threshold, the decision should be YES, and otherwisethe decision should be NO in the step S1405.

Furthermore, not only the path loss for the small-node device with thehighest radio link quality, but also the path loss for the one with thesecond or third highest radio link quality. More specifically,difference between the highest radio link quality and the second highestradio link quality may be utilized in the determination. That is, in acase where the difference is higher than a threshold, the base station200 may establish the D2UE connection 710 (S1406), and in a case wherethe difference is not higher than the threshold, the base station 200may not establish the D2UE connection 710 (S1407). If the difference issmall, the D2UE connection may cause interference with otherconnections. Therefore, such interference issues may be mitigated byutilizing the above control. The above control may apply to a case wherethe small-node device with the second or third highest radio linkquality has D2UE connections with other user equipment in the radioresources.

Referring to FIG. 24, an operation of the mobile communication systemaccording to one or more embodiments of the present invention isdescribed. The operation is related to mobility control in the D2UEconnection 710. The operation may correspond to the step S1103 to S1112in FIG. 16.

Because the steps S1501 to S1503 are almost the same as the steps S1301to S1303. The only difference is that the steps S1301 to S1303 areconducted before the D2UE connection has been established and the stepsS1501 to S1503 are conducted while the D2UE connection is establishedalready. Even if the D2UE connection is established already, the userequipment has to make measurements for known or unknown neighborsmall-node device. In this sense, the measurements in the steps S1301 toS1303 are equivalent to the steps S1501 to S1503. Therefore, explanationfor the steps S1501 to S1503 is omitted.

In the step S1504, the user equipment 100 determines whether or not theneighbor small-node device, which is closer to the user equipment 100than the serving small-node device, is detected. The serving small-nodedevice means the small-node device (the small-node device 500), which iscurrently communicating with the user equipment 100. More specifically,the radio link quality of the neighbor small-node device is higher thanthat of the serving small-node device, it may be determined that theneighbor small-node device is closer to the user equipment 100 than theserving small-node device.

In the determination, hysteresis may be taken into account. Morespecifically, in a case where the following equation is true, it may bedetermined that the neighbor small-node device, which is closer to theuser equipment 100 than the serving small-node device, is detected.(Radio link quality of Neighbor cell)>(Radio link quality of Servingcell)+Hyst

In the equation, Hyst corresponds to the hysteresis. For example,according to one or more embodiments of the present disclosure, Hyst maybe 3 dB. Not only the hysteresis, but also time domain hysteresis may beused. The time domain hysteresis may be called time-to-trigger.

In a case where the neighbor small-node device, which is closer to theuser equipment than the serving small-node device, is detected (stepS1504: YES), the user equipment 100 transmits measurement reports to thebase station 200 in the step S1505. The measurement reports report thatthe neighbor small-node device, which is closer to the user equipmentthan the serving small-node device, is detected.

In the step S1506, the base station 200 transmits handover command tothe user equipment 100. The base station 200 transmits control signalingto the neighbor small-node device 500 for handover preparation.Furthermore, the base station 200 may inform the serving small-nodedevice that the user equipment 100 is handed over to the neighborsmall-node device.

In the step S1507, the user equipment 100 conducts handover to theneighbor small-node device.

In a case where the neighbor small-node device, which is closer to theuser equipment than the serving small-node device, is not detected (stepS1504: NO), the user equipment 100 maintains the D2UE connection withthe small-node device 500 in the step S1508.

Referring to FIG. 25, an operation of the mobile communication systemaccording to one or more embodiments of the present invention isdescribed. The operation is related to mobility control in the D2UEconnection 710. The operation is conducted while the D2UE connection isestablished already.

Because the steps S1601 to S1603 are almost the same as the steps S1301to S1303. The only difference is that the steps S1301 to S1303 areconducted before the D2UE connection is established and the steps S1601to S1603 are conducted while the D2UE connection is established already.Therefore, explanation for the steps S1601 to S1603 is omitted.

In the step S1604, the user equipment 100 determines whether or not pathloss is higher than a threshold. More specifically, the user equipment100 determines whether or not the path loss for the serving small-nodedevice is higher than the threshold. The base station 200 may inform theuser equipment 100 of the threshold by using the control signaling inthe step S1601.

In the above Step S1602 and 1603, the user equipment 100 makesmeasurements for the path loss by using the D2UE pilot signals, butother signals or channels may be used for the path loss measurements.For example, according to one or more embodiments of the presentdisclosure, pilot signals for the channel estimation or demodulation inthe D2UE connection 710 may be used for the path loss measurements. Thepilot signals for the channel estimation or demodulation may providebetter accuracy for path loss measurements than the D2UE pilot signals,which are used for mobility measurements. In case that the path loss arecalculated by using other signals or channels, information on thetransmission power of the other signals or channels may be included inthe other signals or channels. The user equipment 100 may calculate thepath loss based on the received power of the other signals or channelsand the transmission power of the other signals or channels.

In a case where the path loss for the serving small-node device ishigher than the threshold (Step S1604: YES), the user equipment 100transmits measurement reports to the base station 200 in the step S1605.The measurement reports report that the path loss for the servingsmall-node device is higher than the threshold.

In the step S1606, the base station 200 releases the radio resource forthe D2UE connection 710. More specifically, the base station 200 sendscontrol messages to release the D2UE connection 710. As a result, theD2UE connection 710 is released.

In a case where the path loss for the serving small-node device is nothigher than the threshold (Step S1604: NO), the user equipment 100maintains the D2UE connection with the small-node device 500 in the stepS1607.

In the above examples, the path loss is used, but other values whichrepresent the radio link quality may be used. For example, according toone or more embodiments of the present disclosure, at least one of thereceived power of the pilot signal, the SIR of the pilot signal, thereceived quality of the pilot signal and the like may be used. In thiscase, in case that the radio link quality is poorer than a threshold,the decision should be YES, and otherwise the decision should be NO inthe step S1604.

Based on the radio resource management described in FIG. 25, the D2UEconnection, which may interfere with other communications, can beremoved, and therefore good system quality can be maintained.

Referring to FIG. 25A, an operation for the mobile communication systemaccording to one or more embodiments of the present invention isdescribed. The operation is related to mobility control in the D2UEconnection 710. The operation is conducted while the D2UE connection isestablished already.

In the step S1701, the user equipment 100 determines whether or notradio link failure is detected for the BS2UE connection 720.

For example, according to one or more embodiments of the presentdisclosure, the radio link failure may be detected based on expiry of atimer, which is utilized to detect radio link failure in physical layer.The timer may be called T310 in the 3GPP specifications. Alternatively,the radio link failure may be detected based on random access scenarioindication from MAC layer. The radio link failure may be detected basedon indication from RLC layer that the maximum number of retransmissionshas been reached.

In a case where the radio link failure is not detected for the BS2UEconnection 720 (Step S1701: NO), the D2UE connection 710 is maintainedin the step S1702.

In a case where the radio link failure is detected for the BS2UEconnection 720 (Step S1701: YES), the user equipment 100 releases theD2UE connection 710 in the step S1703. In the step S1703, the userequipment 100 may stop transmitting signals in the D2UE connection 710,instead of releasing the D2UE connection 710.

Benefits of the operation described in FIG. 25A are described asfollows. In case that the user equipment 100 cannot communicate with thebase station due to the radio link failure in the BS2UE connection 720,the D2UE connection 710 is also released and therefore the userequipment 100 will not transmit any signals under the conditions wherethe base station 200 cannot control the D2UE connection 710. That is, itcan be avoided that the user equipment 100 transmits interference signalunder the conditions that the base station 200 cannot control the D2UEconnection 710.

Characteristics mentioned above may be described as follows. One of thecharacteristics in one or more embodiments of the present invention is acommunication method in a mobile communication system, in which a mobilestation communicates with a server via a device using D2UE connectionfor offload purposes in addition to using BS2UE connection:

(1st step) Transmitting pilot signals for the D2UE connection in thedevice

(2nd step) Receiving the pilot signals and making the measurements forradio link quality of the D2UE connections in the mobile station

(3rd step) Establishing the D2UE connection based on the measurements inthe device and the mobile station

In the 1st step, transmission timing of the pilot signals are timesynchronized with signals in the BS2UE connection.

One of the characteristics in one or more embodiments of the presentinvention is a communication method in a mobile communication system, inwhich a mobile station communicates with a server via a device usingD2UE connection for offload purposes in addition to using BS2UEconnection:

(1st step) Transmitting pilot signals for the D2UE connection in thedevice

(2nd step) Receiving the pilot signals and making the measurements forpath loss of the D2UE connections in the mobile station

(3rd step) Establishing the D2UE connection based on the measurements inthe mobile station

In the 3rd step, the D2UE connection is not established in case that thepath loss is higher than a predetermined threshold.

Based on one or more embodiments of the invention, high qualitycommunication connectivity, lower power consumption in mobile stations,and less interference in the hybrid D2UE and BS2UE system can beachieved.

The above procedures conducted by the small-node device 500 may beconducted in the D2UE communication section 504. The above proceduresconducted by the user equipment 100 may be conducted in the D2UEcommunication section 104. The above procedures conducted by the basestation 200 may be conducted in the D2UE communication control section204.

In the embodiments, some of the conventional BS2UE operations may beomitted in the D2UE connection 710. More specifically, at least one ofthe following operations may be omitted:

Transmitting broadcast channels in DL

Transmitting common reference signals in DL

Transmitting primary synchronization signals/secondary synchronizationsignals in DL

Transmitting paging signals in DL

Transmitting dedicated RRC signaling related to RRC procedures, such asconnection establishment, connection re-establishment, connection setup,connection reconfiguration, connection release, and the like

Transmitting control signaling for handover, such as control informationof measurement configuration, measurement control, handover command,handover complete and the like

The following operations can be supported by the BS2UE connection 720and the BS2D connection 730, as mentioned above. As a result, thecomplexity of the small-node device 500 can be reduced.

Some others of conventional BS2UE operations may be supported in theD2UE connection 710. More specifically, at least one of the followingoperations may be supported:

Transmitting PDCCH in DL

Transmitting PHICH in DL

Transmitting PCFICH in DL

Transmitting PUCCH in UL

Transmitting PUSCH in UL

Transmitting PRACH in UL

Uplink power control

DL power control

Adaptive modulation and coding for DL and UL

DRX

HARQ

(An example#1, according to one or more embodiments, for data handlingduring handover in the D2UE connection 710)

In case that the user equipment 100 makes the handover from one cell (asource cell) to another cell (a target cell), there are in general someoptions for handling data which are buffered in the source cell.

One option is that the source cell drops the data which are buffered inthe source cell. In this option, user data throughput is degraded afterthe handover, because the dropped data may affect TCP layer behaviors.For example, TCP layer may try to decrease TCP window size, because itregards the dropped data as the ones caused by congestion. However, thesource cell does not forward the buffered data to the target cell, andtherefore processing complexity in the source cell and target cell canbe minimized.

Another option is that the source cell forwards to the target cell thedata which are buffered in the source cell. In this option, user datathroughput can be maintained even if the handover is conducted. But, theprocessing complexity in the source cell and target cell increases.

In terms of the hybrid D2UE and BS2UE system described above, thesmall-node device 500 provides a small coverage area for the userequipment 100 in the D2UE connection 710, and therefore if the number ofhandovers in the D2UE connection increases due to high mobility and datadropping happens in each handover, the user data throughput in the D2UEconnection may be degraded.

Hereinafter, handover in the D2UE connection is called “D2UE handover”.That is, “D2UE handover” corresponds to handover wherein the userequipment 100 changes “D2UE connection with one small-node device” to“D2UE connection with another small-node device”.

If the data forwarding is conducted from a source small-node device to atarget small-node device in each D2UE handover, the user data throughputcan be maintained, but complexity of each small-node device increases.

In the following, some embodiments, where such user throughputdegradation can be avoided and complexity of small-node device can beminimized to some extent, are described. Some embodiments are based onthe architecture shown in FIG. 9, as described below.

FIG. 29 illustrates almost the same system architecture as the one inFIG. 9. The difference between FIG. 9 and FIG. 29 is that the small-nodedevices, which are connected to a center-small-node device 510, arelocated in the coverage areas provided by two base stations (the basestation 200A and the base station 200B). It is noted that the number ofthe base stations is just an example, and it may be one or more thantwo. Furthermore, in FIG. 29, only the server 600 and the core network400 are illustrated for simplicity, but the center-small-node device 500may connect to the interne and the server 610 in some embodiments.

Here, the total coverage area provided by the small-node devices500A/500B/500C/500D/500E is almost the same as the one provided by thebase stations 200A/200B, as illustrated in FIG. 29.

In this example, according to one or more embodiments, one PDCP/RLClayer operation for the small-node devices 500A/500B/500C/500D/500E isconducted in the center-small-node device 510, as illustrated in FIG.30.

In FIG. 30, the small-node device 500A, the small-node device 500B andthe center-small-node device 510 are illustrated, and other small-nodedevices are omitted. Other small-node devices have the sameconfiguration, function and state as the small-node devices 500A/500B.

Comparison between the small-node device 500 illustrated in FIG. 11 andthe small-node device 500A/the center-small-node device 510 in FIG. 30is described in the following. The D2UE communication section 504 inFIG. 11 is divided to a D2UE L1 communication section 504A-1 and a D2UERRC/MAC/RLC/PDCP operation section 504-2. The D2UE L1 communicationsection 504A-1 is located in the small-node device 500A, and the D2UERRC/MAC/RLC/PDCP operation section 504-2 is located in thecenter-small-node device 510. The Backhaul communication section 506 islocated in the center-small-node device 510, instead of the small-nodedevice 500A.

The BS2D communication section 502A, the D2UE RRC/MAC/RLC/PDCP operationsection 504-2, and the Backhaul communication section 506 are connectedto each other, and communicate with each other, similarly to the BS2Dcommunication section 502, the D2UE communication section 504, and theBackhaul communication section 506 in FIG. 11.

The D2UE L1 communication section 504A-1 is connected to the D2UEMAC/RLC/PDCP communication section 504-2, and they communicate with eachother. A connection between the D2UE L1 communication section 504A-1 andthe D2UE MAC/RLC/PDCP communication section 504-2 may be an opticalfiber.

The D2UE L1 communication section 504A-1 may be a remote radio head. Inthis case, the D2UE MAC/RLC/PDCP communication section 504-2 conductsbaseband processing, such as PDCP operation/RLC operation/MACoperation/coding/decoding and the like, and transmits digitalinformation for baseband signals to the D2UE L1 communication section504A-1 in the optical fiber. The D2UE L1 communication section 504A-1converts the digital information to radio frequency signals andtransmits them after amplifying the radio frequency signals.Furthermore, the D2UE L1 communication section 504A-1 receives radiofrequency signals transmitted by the user equipment 100, converts theradio frequency signals to digital information for baseband signals, andtransmits the digital information to the D2UE MAC/RLC/PDCP communicationsection 504-2 in the optical fiber.

Alternatively, some parts of the baseband processing may be conducted bythe D2UE L1 communication section 504A-1, and others may be conducted bythe D2UE MAC/RLC/PDCP communication section 504-2 conducts. How todivide the baseband processing between the D2UE L1 communication section504A-1 and the D2UE MAC/RLC/PDCP communication section 504-2 is notlimited to the above examples.

Description of the BS2D communication section 502A is almost the same asthe one of the BS2D communication section 502 in FIG. 11, and thereforeis omitted here.

Functions supported by the D2UE L1 communication section 504A-1 and theD2UE RRC/MAC/RLC/PDCP operation section 504-2 are almost the same as theones supported by the D2UE communication section 504 in FIG. 11.

More specifically, the D2UE RRC/MAC/RLC/PDCP operation section 504-2manages the D2UE connection 710 between the small-node device 500 andthe user equipment 100, i.e. the D2UE RRC/MAC/RLC/PDCP operation section504-2 establishes/configures/re-configures/re-establishes/releases theD2UE connection 710 between the small-node device 500 and the userequipment 100. The management of the D2UE connection 710 is based on thecontrol signaling transmitted by the base station 200. The D2UERRC/MAC/RLC/PDCP operation section 504-2 manages the D2UE connection forthe small-node device 500A/500B/500C/500D/500E, which are connected tothe center-small-node device 510.

The D2UE RRC/MAC/RLC/PDCP operation section 504-2 buffers data to betransmitted in downlink and data received in uplink for the small-nodedevices 500A/500B/500C/500D/500E. Because the D2UE RRC/MAC/RLC/PDCPoperation section 504-2 has one section to buffer data for thesmall-node devices 500A/500B/500C/500D/500E, which are connected to thecenter-small-node device 510, no data drops occur and no data forwardingis needed in case of the D2UE handover among the small-node devices500A/500B/500C/500D/500E.

Referring to FIG. 17, more specific operations for data buffering areexplained below. The D2UE RRC/MAC/RLC/PDCP operation section 504-2buffers data to be transmitted to the user equipment 100, in case theuser equipment 100 makes the D2UE handover from the small-node device500A to the small-node device 500B. The small-node device 500A and 500Bcorrespond to the source small-node device 500A and the targetsmall-node device 500B, respectively.

Just before or just after or at the same timing as S1108, the D2UE L1communication section 504A-1 stops transmitting downlink data, and thedownlink data is buffered in the D2UE RRC/MAC/RLC/PDCP operation section504-2. Just after or at the same time as the step S1111, the D2UE L1communication section 504B-1 starts transmitting the downlink data whichis buffered in the D2UE RRC/MAC/RLC/PDCP operation section 504-2.Alternatively, the D2UE L1 communication section 504B-1 may starttransmitting the downlink data which is buffered in the D2UERRC/MAC/RLC/PDCP operation section 504-2 just after or at the same timeas the step S1112.

That is, data dropping in a source small-node device and data forwardingfrom a source small-node device to a target small-node device can beavoided by buffering data in a common buffer in the D2UERRC/MAC/RLC/PDCP operation section 504-2.

The D2UE RRC/MAC/RLC/PDCP operation section 504-2 may buffer uplink dataas well as downlink data for the D2UE connection.

The buffer in the D2UE RRC/MAC/RLC/PDCP operation section 504-2 may be abuffer of MAC layer or may be a buffer of RLC layer or may be a bufferof PDCP layer. Alternatively, the buffer may be a mixture of at leastone of MAC layer buffer, RLC layer buffer and PDCP layer buffer. Morespecifically, the buffer may be a buffer of PDCP/RLC layer.Alternatively, the buffer may be a buffer of PDCP/RLC/MAC layer.

The D2UE RRC/MAC/RLC/PDCP operation section 504-2 may not have onesection to buffer data, but more than one section to buffer data.Configurations for the section to buffer data may not be limited to onespecific configuration, and various kinds of configurations may bepossible. For example, according to one or more embodiments of thepresent disclosure, the D2UE RRC/MAC/RLC/PDCP operation section 504-2may have two sections to buffer data, and the two sections very closelycommunicate with each other so that the two sections can be regarded asone logical section to buffer data. The number of two is just anexample, and the D2UE RRC/MAC/RLC/PDCP operation section 504-2 may havemore than two sections to buffer data.

The D2UE RRC/MAC/RLC/PDCP operation section 504-2 may conduct a linkadaptation for the D2UE connection 710, such as power control andadaptive modulation and coding. The link adaptation may be conductedbased on parameters which are signaled from the base station 200. TheD2UE RRC/MAC/RLC/PDCP operation section 504-2 may conduct a linkadaptation of the D2UE connection for the small-node device500A/500B/500C/500D/500E, which are connected to the center-small-nodedevice 510. Alternatively, the D2UE L1 communication section 504A-1 mayconduct a link adaptation for the D2UE connection 710 for the small-nodedevice 500A.

The D2UE L1 communication section 504A-1 transmits data to the userequipment 100 and receives data from the user equipment 100 utilizingthe D2UE connection 710 between the small-node device 500A and the userequipment 100. As described above, data for some of the radio bearersmay be transmitted in the D2UE connection 710.

The D2UE L1 communication section 504A-1 transmits the downlink data tothe user equipment 100 using the D2UE connection 710. The downlink datais transferred from the server 600 via the core network 400, theBackhaul communication section 506 and the D2UE RRC/MAC/RLC/PDCPoperation section 504-2.

The D2UE L1 communication section 504A-1 receives the uplink data fromthe user equipment 100 using the D2UE connection 710. The uplink data istransferred to the server 600 via the D2UE RRC/MAC/RLC/PDCP operationsection 504-2, the Backhaul communication section 506 and the corenetwork 400.

The D2UE L1 communication section 504A-1 also conducts measurements forthe D2UE connection 710 for the small-node device 500A. Description ofthe measurements is the same as the one in the D2UE communicationsection 504, and therefore is omitted here. The D2UE L1 communicationsection 504A-1 reports the measurement results to the base station 200via the D2UE RRC/MAC/RLC/PDCP operation section 504-2, the BS2Dcommunication section 502 and the BS2D connection 730.

Components enclosed in a dashed line in FIG. 31 may be regarded as alogical small-node device 500A, which has the same configuration,function and state as the small-node device 500 described in FIG. 11.

The BS2D communication section 502A is located in the small-node device500A in FIG. 30, but some parts of the BS2D communication section 502Amay be located in the small-node device 500A, and others are located inthe center-small-node device 510, similarly to the D2UE L1 communicationsection 504A-1 and the D2UE RRC/MAC/RLC/PDCP operation section 504-2.

Alternatively, the BS2D communication section 502 may be located in thecenter-small-node device 510, as illustrated in FIG. 32. In thisarchitecture, the BS2D communication section 502 supports functions ofthe BS2D communication sections 502A/502B/502C/502D/502E for thesmall-node devices 500A/500B/500C/500D/500E, respectively.

Alternatively, only buffer section 504-3 may be located in thecenter-small-node device 510. The other functions for the D2UE L1communication section 504A-1 and the D2UE RRC/MAC/RLC/PDCP operationsection 504-2, which are described in FIG. 30, may be located in thesmall-node device 500A, as illustrated in FIG. 32A. In the figure, D2UEcommunication section 504A handles the other functions for the D2UE L1communication section 504A-1 and the D2UE RRC/MAC/RLC/PDCP operationsection 504-2, which are described in FIG. 30. The BS2D communicationsection 502A, the D2UE communication section 504A, and the buffersection 504-3 are connected with each other, and communicate with eachother.

The buffer section 504-3 may be a buffer of PDCP/RLC layer.Alternatively, the buffer section 504-3 may be a buffer of MAC layer ora buffer of RLC layer or may be a buffer of PDCP layer. Alternatively,the buffer section 504-3 may be a mixture of at least one of MAC layerbuffer, RLC layer buffer and PDCP layer buffer. Alternatively, thebuffer section 504-3 may be a buffer of PDCP/RLC/MAC layer.

More specifically, the center-node small-node device 510 may have a PDCPoperation section/Buffer section 504-5 and the small-node device 500Amay have a D2UE RRC/L1/MAC/RLC communication section 504A-4, asillustrated in FIG. 32B. That is, the PDCP operation section/Buffersection 504-5 handles the PDCP operation and buffers downlink data anduplink data in PDCP layer, and the D2UE RRC/L1/MAC/RLC communicationsection 504A-4 handles the other functions for the D2UE L1 communicationsection 504A-1 and the D2UE RRC/MAC/RLC/PDCP operation section 504-2,which are described in FIG. 30. The D2UE RRC/L1/MAC RLC communicationsection 504A-4 handles:

Managing the D2UE connection 710 between the small-node device 500 andthe user equipment 100.

Establishing/configuring/re-configuring/re-establishing/releasing theD2UE connection 710.

Handling L1/MAC/RLC operations for the D2UE connection 710.

Description for the small-node device 500A/the center-small-node device510 is the same as the one for the small-node device 500B/thecenter-small-node device 510, and therefore it is omitted.

In summary, the data dropping does not occur and the data forwarding isnot needed in the D2UE handover from the small-node device 500A to thesmall-node device 500B in a set of the small-node devices 500A/500B andthe center-small-node device 510. The center-small-node device 510 canbuffer data to be transferred in the D2UE connection between the userequipment 100 and the small-node device 500A and data to be transferredin the D2UE connection between the user equipment 100 and the small-nodedevice 500B.

(An example#2, according to one or more embodiments:Multiple-D2UE-connection operation)

In case the user equipment 100 makes the handover from one cell (asource cell) to another cell (a target cell), some control signals forthe handover are transmitted. The control signals correspond to RRCsignals in conventional cellular network. For example, according to oneor more embodiments of the present disclosure, the user equipment 100transmits to the base station a measurement report which indicates thata neighbor cell radio link quality is better than the serving cell radiolink quality. Furthermore, the base station transmits to the userequipment a handover command which instructs that the user equipment 100should make the handover to the neighbor cell which has better radiolink quality than the serving cell.

In terms of the hybrid D2UE and BS2UE system described above, theoperation shown in FIG. 17 is conducted for the D2UE handover. Thesmall-node device 500 provides a small coverage area for the userequipment 100 in the D2UE connection 710. Therefore in case the numberof handovers in the D2UE connection increases due to high mobility, alot of control signals are transmitted frequently. It may increasecontrol signal processing complexity in the base station 200.Furthermore, if the base station 200 may exchange control signals with acore node for the handover, control signal processing complexity in thecore node also increases.

In the following, some embodiments, where such control signal processingcomplexity can be minimized, are described. Some embodiments are basedon the architecture shown in FIG. 29.

In this example, according to one or more embodiments, it is assumedthat the user equipment 100 has multiple connections with multiplesmall-node devices, instead of having a single connection with onesmall-node device. The control signal processing complexity can bereduced by having such multiple connections with multiple small-nodedevices.

For example, according to one or more embodiments of the presentdisclosure, if the user equipment 100 has multiple connections with thesmall-node devices 500A/500B/500C/500D/500E in FIG. 29, control signalsfor D2UE handover are not transmitted for the D2UE handover from thesmall-node device 500A to 500B, from the small-node device 500B to 500C,from the small-node device 500C to 500D, and from the small-node device500D to 500E. That is, transmitting control signals for four D2UEhandovers can be omitted, and as a result the control signal processingcomplexity can be reduced.

Of course, in case the user equipment 100 cannot communicate with allthe small-node devices simultaneously, it should be decided at one timeoccasion which small-node device the user equipment 100 shouldcommunicate with. Here, “communicating with a small-node device” means“transmitting data to and receive data from a small-node device”. But,such decision can be conducted in a lower layer such as the L1/L2 layer,instead of the RRC layer. More specifically, such a decision ofselecting the small-node device with which the user equipment 100 shouldcommunicate may be regarded as a part of MAC layer scheduling.Alternatively, such a decision of selecting the small-node device withwhich the user equipment 100 should communicate may be regarded as apart of transmission point selection in physical layer.

In FIG. 33, the small-node device 500A, the small-node device 500B andthe center-small-node device 510 are illustrated, and other small-nodedevices are omitted. Other small-node devices have the sameconfiguration, function and state as the small-node devices 500A/500B.Furthermore, the base station 200A and the user equipment 100 are alsoillustrated in FIG. 33.

The small-node devices 500A/500B and the center-small-node device 510are almost the same as those in FIG. 32, and therefore only additionalfunctions/operations compared to those in FIG. 32 are described below.

The user equipment 100 is almost the same as the one in FIG. 12, andtherefore only additional functions/operations compared to those in FIG.12 are described below.

The base station 200A is almost the same as the base station 200 in FIG.13, and therefore only additional functions/operations compared to thosein FIG. 13 are described below.

FIG. 34 illustrates DL transmissions of one or more embodiments of thepresent disclosure with multiple D2UE connections.

In this example, according to one or more embodiments of the presentdisclosure, it is assumed that the user equipment 100 has multipleconnections (a D2UE connection 710A and a D2UE connection 710B) with thesmall-node device 500A and the small-node device 500B, respectively. Thenumber of multiple connections is two as an example in the followingdescription and it may not be limited to two. That is, it may be morethan two.

In Case #1, the small-node device 500A transmits DL signals to the userequipment 100 in the D2UE connection 710A. In Case #2, the small-nodedevice 500B transmits DL signals to the user equipment 100 in the D2UEconnection 710B. In Case #3, the small-node device 500A and thesmall-node device 500B transmit DL signals to the user equipment 100simultaneously.

More specifically, the D2UE L1 communication section 504A-1 transmitsthe DL signals in the small-node device 500A, and the D2UE L1communication section 504B-1 transmits the DL signals in the small-nodedevice 500B. And, the D2UE communication section 104 receives the DLsignals in the user equipment 100.

Here, the DL signals are dedicated to the user equipment 100. That is,the DL signals are signals specific to the user equipment 100. Forexample, according to one or more embodiments of the present disclosure,the DL signals are scrambled by a random sequence which is specific tothe user equipment 100. On the other hand, the DL signals are notdedicated to the small-node device 500A or to the small-node device500B. For example, according to one or more embodiments of the presentdisclosure, the DL signals are not scrambled by a random sequence whichis specific to the small-node device 500A or to the small-node device500B. In other words, the small-node device 500A and the small-nodedevice 500B utilize the same random sequence for scrambling.

The random sequence specific to the user equipment 100 may be generatedbased on identification number of the user equipment 100. Alternatively,the random sequence specific to the user equipment 100 may be indicatedby the base station 200A or the base station 200B. The information ofthe random sequence may be a part of the information of downlinkphysical shared channel for the D2UE connection 710.

As a result, the user equipment 100 does not need to identify whichsmall-node device is transmitting the DL signals. That is, the userequipment does not see difference among Case #1, Case #2, and Case #3when it receives the DL signals.

Pilot signals, which are used in channel estimation for DL signals, arealso transmitted with the DL signals, and the pilot signals arescrambled similarly to the DL signals. That is, the pilot signalstransmitted from each small-node device are scrambled by a randomsequence which is specific to the user equipment 100. The small-nodedevice 500A utilizes the same random sequence for scrambling the pilotsignals as the small-node device 500B, in terms of the user equipment100. The pilot signals may be called “reference signals” or“demodulation reference signal”.

The D2UE MAC/RLC/PDCP communication section 504-2 selects whichsmall-node device should transmit DL signals to the user equipment 100in one time frame. The time frame may be the same as the sub-frame inLTE. The sub-frame in LTE corresponds to 1 msec. The time frame may be10 msec or other values, instead of 1 msec, and may not be limited tothe above examples

For example, according to one or more embodiments of the presentdisclosure, the D2UE MAC/RLC/PDCP communication section 504-2 selectsthe small-node device 500A as a small-node device which should transmitDL signals to the user equipment 100, processes baseband signals of theDL signals, and transmits the baseband signals to the D2UE L1communication section 504A-1 for a time frame. The D2UE L1 communicationsection 504A-1 converts the baseband signals to radio frequency signals,amplifiers the radio frequency signals and transmits them.

The D2UE MAC/RLC/PDCP communication section 504-2 selects a small-nodedevice, which should transmit DL signals to the user equipment 100, byutilizing radio link quality of each D2UE connection. The radio linkquality may be at least one of signal-to-interference, path loss,received power, transmitted power and the like. The radio link qualitymay be calculated by utilizing received D2UE pilot signals.

More specifically, in case the radio link quality between the userequipment 100 and the small-node device 500A is better than the onebetween the user equipment 100 and the small-node device 500B, the D2UEMAC/RLC/PDCP communication section 504-2 selects the small-node device500A as shown in Case #1.

Alternatively, in case the path loss between the user equipment 100 andthe small-node device 500A is larger than the one between the userequipment 100 and the small-node device 500B, the D2UE MAC/RLC/PDCPcommunication section 504-2 selects the small-node device 500B as shownin Case #2.

Alternatively, in case the D2UE pilot received power between the userequipment 100 and the small-node device 500A is almost the same as theone between the user equipment 100 and the small-node device 500B and itis not so large, the D2UE MAC/RLC/PDCP communication section 504-2selects both the small-node devices 500A and the small-node device 500Bas shown in Case #3 so that the user equipment 100 can receive the DLsignals with higher received power.

The radio link quality may be estimated by received D2UE pilot signals.Alternatively, the radio link quality may be estimated by received ULpilot signals, such as sounding reference signals.

The D2UE MAC/RLC/PDCP communication section 504-2 selects a small-nodedevice, which should transmit DL signals to the user equipment 100,among the small-node devices which are indicated by a control signaltransmitted by the base station 200. The small-node devices may becalled a “small-node device group”. That is, the base station 200notifies the D2UE MAC/RLC/PDCP communication section 504-2 ofidentification number of each small-node device, which is included inthe small-node device group, and the D2UE MAC/RLC/PDCP communicationsection 504-2 selects one or some of the small-node devices as the oneswhich actually communicate with the user equipment 100 at a time frame.The base station 200 may notify the user equipment 100 as well of theidentification number of each small-node device, which is included inthe small-node device group. The control signal is described later.

As a result, the best radio link quality transmission point whichtransmits DL signals can be selected dynamically without D2UE handovers.In other words, the best radio link quality transmission point whichtransmits DL signals can be selected dynamically without any RRC layercontrol signals.

FIG. 35 illustrates UL transmissions of one or more embodiments of thepresent disclosure with multiple D2UE connections.

In this example according to one or more embodiments of the presentdisclosure, it is assumed that the user equipment 100 has multipleconnections (a D2UE connection 710A and a D2UE connection 710B) with thesmall-node device 500A and the small-node device 500B, respectively. Thenumber of multiple connections is two as an example in the followingdescription and it may not be limited to two. That is, it may be morethan two.

In Case #1, the small-node device 500A receives UL signals transmittedby the user equipment 100 in the D2UE connection 710A. In Case #2, thesmall-node device 500B receives UL signals transmitted by the userequipment 100 in the D2UE connection 710B. In Case #3, the small-nodedevice 500A and the small-node device 500B receive UL signalstransmitted the user equipment 100 simultaneously.

More specifically, the D2UE L1 communication section 504A-1 receives theUL signals in the small-node device 500A, and the D2UE L1 communicationsection 504B-1 receives the UL signals in the small-node device 500B.And, the D2UE communication section 104 transmits the UL signals in theuser equipment 100.

Here, the UL signals are dedicated to the user equipment 100. That is,the UL signals are signals specific to the user equipment 100. Forexample, according to one or more embodiments of the present disclosure,the UL signals are scrambled by a random sequence which is specific tothe user equipment 100. On the other hand, the UL signals are notdedicated to the small-node device 500A or to the small-node device500B. For example, according to one or more embodiments of the presentdisclosure, the UL signals are not scrambled by a random sequence whichis specific to the small-node device 500A or to the small-node device500B. In other words, the small-node device 500A and the small-nodedevice 500B utilize the same random sequence for scrambling.

The random sequence specific to the user equipment 100 may be generatedbased on identification number of the user equipment 100. Alternatively,the random sequence specific to the user equipment 100 may be indicatedby the base station 200A or the base station 200B. The information ofthe random sequence may be a part of the information of uplink physicalshared channel for the D2UE connection 710.

As a result, the user equipment 100 does not need to identify to whichsmall-node device it is transmitting the UL signals. That is, the userequipment does not see difference among Case #1, Case #2, and Case #3when it transmits the UL signals.

Pilot signals, which are used in channel estimation for UL signals, arealso transmitted with the UL signals, and the pilot signals arescrambled similarly to the UL signals. That is, the pilot signalstransmitted from each small-node device are scrambled by a randomsequence which is specific to the user equipment 100. The small-nodedevice 500A utilizes the same random sequence for scrambling the pilotsignals as the small-node device 500B, in terms of the user equipment100. The pilot signals may be called “reference signals” or“demodulation reference signal”.

The D2UE MAC/RLC/PDCP communication section 504-2 selects whichsmall-node device should receive UL signals transmitted by the userequipment 100 in one time frame. The time frame may be the same as thesub-frame in LTE. The sub-frame in LTE corresponds to 1 msec. The timeframe may be 10 msec or other values, instead of 1 msec, and may not belimited to the above examples.

For example, according to one or more embodiments of the presentdisclosure, the D2UE MAC/RLC/PDCP communication section 504-2 selectsthe small-node device 500A as a small-node device which should receiveUL signals to the user equipment 100, processes baseband signals of ULgrant signals for assigning the UL signals' radio resource, andtransmits the baseband signals to the D2UE L1 communication section504A-1 for a time frame. The D2UE L1 communication section 504A-1converts the baseband signals to radio frequency signals, amplifiers theradio frequency signals and transmits them. The user equipment 100receives the UL grant signals and transmits the UL signals by utilizingthe radio resource indicated by the UL grant signals. Transmissiontiming of UL signals may be delayed compared to reception timing of theUL grant signals. For example, according to one or more embodiments ofthe present disclosure, in case the UL grant signals are received atSub-frame #N, the UL signals may be transmitted at Sub-frame #N+4. TheD2UE L1 communication section 504A-1 receives radio frequency signals ofthe UL signals, converts them to baseband signals, and transmits them tothe D2UE MAC/RLC/PDCP communication section 504-2. The D2UE MAC/RLC/PDCPcommunication section 504-2 receives the baseband signals and conductbaseband processing, such as decoding, MAC layer operations, RLC layeroperations, PDCP layer operations, and the like.

The D2UE MAC/RLC/PDCP communication section 504-2 selects a small-nodedevice, which should receive UL signals transmitted by the userequipment 100, by utilizing radio link quality of each D2UE connection.The radio link quality may be at least one of signal-to-interference,path loss, received power, transmitted power and the like. The radiolink quality may be calculated by utilizing received D2UE pilot signals.

More specifically, in case the radio link quality between the userequipment 100 and the small-node device 500A is better than the onebetween the user equipment 100 and the small-node device 500B, the D2UEMAC/RLC/PDCP communication section 504-2 selects the small-node device500A as shown in Case #1.

Alternatively, in case the path loss between the user equipment 100 andthe small-node device 500A is larger than the one between the userequipment 100 and the small-node device 500B, the D2UE MAC/RLC/PDCPcommunication section 504-2 selects the small-node device 500B as shownin Case #2.

Alternatively, in case the D2UE pilot received power between the userequipment 100 and the small-node device 500A is almost the same as theone between the user equipment 100 and the small-node device 500B and itis not so large, the D2UE MAC/RLC/PDCP communication section 504-2selects both the small-node devices 500A and the small-node device 500Bas shown in Case #3 so that total received power of the UL signals inthe small-node devices 500A and 500B can increase.

The radio link quality may be estimated by received D2UE pilot signals.Alternatively, the radio link quality may be estimated by received ULpilot signals, such as sounding reference signals.

The D2UE MAC/RLC/PDCP communication section 504-2 selects a small-nodedevice, which should receive UL signals to the user equipment 100, amongthe small-node devices which are indicated by a control signaltransmitted by the base station 200. The small-node devices may becalled a “small-node device group”. That is, the base station 200notifies the D2UE MAC/RLC/PDCP communication section 504-2 ofidentification number of each small-node device, which is included inthe small-node device group, and the D2UE MAC/RLC/PDCP communicationsection 504-2 selects one or some of the small-node devices as the oneswhich actually communicate with the user equipment 100 at a time frame.The base station 200 may notify the user equipment 100 as well of theidentification number of each small-node device, which is included inthe small-node device group. The control signal is described later.

As a result, the best radio link quality transmission point whichreceives UL signals can be selected dynamically without D2UE handovers.In other words, the best radio link quality reception point whichreceives UL signals can be selected dynamically without any RRC layercontrol signals.

In the above description for UL signals, the D2UE MAC/RLC/PDCPcommunication section 504-2 may select a small-node device whichtransmits UL grant signals, instead of selecting a small-node devicewhich receives UL signals transmitted by the user equipment.

As mentioned above, in case the user equipment 100 has D2UE connectionswith a lot of small-node devices, the number of control signals for D2UEhandover can be reduced. In the above mentioned embodiments, the D2UEpilot signals may need to be detected not only with high radio linkquality, but also with low radio link quality.

As illustrated in FIG. 36, there is a case where some of small-nodedevices are connected to one center-small-node device and others areconnected to another center-small-node device. More specifically, thesmall-node devices 500A/500B/500C are connected to the center-small-nodedevice 510A, and the small-node device 500D/500C are connected to thecenter-small-node device 510B. In this case, the user equipment 100cannot have multiple connections with the small-node device 510C andwith the small-node device 510D simultaneously, because thecenter-small-node device connected to the small-node device 510C isdifferent from the one connected to the small-node device 510D.

That is, the user equipment 100 cannot always have multiple connectionswith all the small-node devices which are closed to the user equipment100 in terms of radio link quality. Therefore, the user equipment 100needs to be informed of information for small-node devices with whichthe user equipment 100 can have multiple D2UE connections. Theinformation may be identification number of small-node device.Alternatively, the information may be identification number of D2UEpilot signal.

The information for small-node devices with which the user equipment 100can have multiple D2UE connections may be regarded as the informationfor small-node devices with which the user equipment 100 cancommunicate.

In some embodiments, the base station 200 transmits to the userequipment 100 a control signal for indicating the information forsmall-node devices which the user equipment 100 can have multiple D2UEconnections. In case illustrated in FIG. 36, for example, according toone or more embodiments of the present disclosure, the control signalnotify the user equipment of the identification number of the small-nodedevice 500A/500B/500C, which the user equipment can have multipleconnections with.

More specifically, the information may be included in the controlsignaling of the step A804 c in FIG. 14A. Alternatively, it may beincluded in the control signaling of the step A803 a. Alternatively, theinformation may be included in the control signaling of the step S1005in FIG. 16. Alternatively, it may be included in the step S1108 in FIG.17.

Alternatively, the information for small-node devices which the userequipment 100 can have multiple D2UE connections may be transmitted tothe user equipment 100 as a MAC layer control signal in the BS2UEconnection 720.

Furthermore, the base station 200 may transmit the center-small-nodedevice 510 control signals for indicating the information for small-nodedevices which the user equipment 100 can have multiple D2UE connections.

More specifically, the information may be included in the controlsignaling of the step A804 a in FIG. 14A. Alternatively, it may beincluded in the control signaling of the step S1004 in FIG. 16.Alternatively, it may be included in the control signaling of the stepS1106 in FIG. 17.

The information may be included in a control signal which is exchangedwith two base stations, in case that the user equipment 100 makes ahandover between the two base stations in the BS2UE connection. Thecontrol signal may be called “handover request”.

In addition to the information for the small-node devices which the userequipment 100 can have multiple D2UE connections, information for therandom sequence for scrambling the DL signals/UL signals may be includedin the above mentioned control signaling.

In some other embodiments, the center-small-node device 510 may belocated in the base station 200A, as illustrated in FIG. 37. Thearchitecture may be regarded as a mixture of FIGS. 8 and 9. In case thatthe base station 200A has a lot of baseband processing capability, theconfiguration in FIG. 37 is also feasible. The difference from theconventional carrier aggregation is that the user equipment 100 cancommunicate with the small-node devices, such as the small-node devices500D/500E, when the user equipment 100 is located in the coverage areaof the base station 200B, instead of the base station 200A. This isbecause the base station 200B and the center-small-node device do nothave to have a single PDCP/RLC operation in the hybrid D2UE and BS2UEarchitecture and do not have to have very tight inter-working betweenthe D2UE and BS2UE link from a physical and MAC layer point of view.

In the figure, the center-small-node device 510 is located in the basestation 200A, but it is not limited to the above example. Thecenter-small-node device 510 may be located in the base station 200B.

One of the characteristics in one or more embodiments of the presentinvention is a device in a mobile communication system, in which amobile station communicates with a server, comprising a 1stcommunication unit for communicating with a first radio base stationusing a first; multiple 2nd communication units for communicatingwirelessly with the mobile station using multiple second links,respectively; a buffering unit for buffering data; and a 3rdcommunication unit for communicating with the server using a third link;wherein the 1st communication unit exchanges with the radio base stationa first control signal for establishing the multiple second links; themultiple 2nd communication units establish the multiple second links,respectively, on receiving the first control signal, the multiple 2ndcommunication units receive a first data in the multiple second links,respectively, which is sent by the mobile station to the server, the 3rdcommunication unit transmit the first data to the server in the thirdlink, and the 3rd communication unit receives a second data which issent by the server to the mobile station, the multiple 2nd communicationunit transmit the second data to the mobile station, the buffering unitbuffers the first data and the second data for the multiple 2ndcommunication units.

Here, the radio base station corresponds to the base station 200. Themobile station corresponds to the user equipment 100. The devicecorresponds to a set of the small-node devices 500A/500B and thecenter-small-node device 510. The first link corresponds to the BS2Dconnection 730. The second link corresponds to the D2UE connection 710.The third link corresponds to the backhaul connection 750.

Here, the multiple second links may be regarded as one link, because themobile-station-specific signals are transmitted in the multiple secondlinks as described above.

In the above mentioned device, one of the multiple 2nd communicationunits transmits the second data to the mobile station at a time frame.The time frame may be 1 sub-frame or 1 radio frame.

In the above mentioned device, more than one of the multiple 2ndcommunication units transmits the second data to the mobile station at atime frame. The time frame may be 1 sub-frame or 1 radio frame.

In the above mentioned device, the first data and the second data arescrambled by a sequence specific to the mobile station in the secondlinks.

In the above mentioned device, identification number of each of themultiple 2nd communication units is included in the first controlsignal.

One of the characteristics in one or more embodiments of the presentinvention is a mobile station in a mobile communication system, in whicha mobile station communicate with a server, comprising a 1stcommunication unit for communicating wirelessly with a first radio basestation using a first link; and a 2nd communication unit forcommunicating wirelessly with multiple devices using multiple secondlinks, respectively; wherein the 1st communication unit exchanges withthe first radio base station a first control signal for establishing themultiple second links, the 2nd communication unit establishes themultiple second links on receiving the first control signal, the 2ndcommunication unit transmits a first user data with the finaldestination to the server via the multiple second links, and the 2ndcommunication unit receives a second user data originated from theserver via the multiple second links.

Here, the radio base station corresponds to the base station 200. Themobile station corresponds to the user equipment 100. The devicecorresponds to the small-node device 500. The first link corresponds tothe BS2UE connection 720. The second link corresponds to the D2UEconnection 710.

Here, the multiple second links may be regarded as one link, because themobile-station-specific signals are transmitted in the multiple secondlinks as described above.

In the above mentioned mobile station, one of the devices transmits thesecond user data to the mobile station at a time frame.

In the above mentioned mobile station, more than one of the devicestransmits the second user data to the mobile station at a time frame.

In the above mentioned mobile station, the first data and the seconddata are scrambled by a sequence specific to the mobile station in themultiple second links.

In the above mentioned mobile station, identification number of each ofthe devices is included in the first control signal.

One of the characteristics in one or more embodiments of the presentinvention is a radio base station in a mobile communication system, inwhich a mobile station communicate with a server, comprising a 1stcommunication unit for communicating with multiple devices using a firstlink; a 2nd communication unit for communicating wirelessly with amobile station using a second link; and a control unit for determininghow to configure multiple third links between the multiple devices andthe mobile station, respectively; wherein the 1st communication unitexchanges with the multiple devices a first control signal forestablishing the multiple third links, the 2nd communication unitexchanges with the mobile station a second control signal forestablishing the multiple third links, a first data is transferred fromthe mobile station with the final destination to the server via themultiple third links, a second data originated from the server istransferred to the mobile station via the multiple third links, andidentification number of each of the multiple devices is included in thefirst control signal and second control signal.

Here, a radio base station corresponds to the base station 200. A mobilestation corresponds to the user equipment 100. A device corresponds tothe small-node device 500. A first link corresponds to the BS2Dconnection 730. A second link corresponds to the BS2UE connection 720.The third link corresponds to the D2UE connection 710.

Here, the multiple third links may be regarded as one link, because themobile-station-specific signals are transmitted in the multiple thirdlinks as described above.

The operation of the above-described base station 200, the userequipment 100 and the small-node device 500 may be implemented by ahardware, may also be implemented by a software module executed by aprocessor, and may further be implemented by the combination of theboth.

The software module may be arranged in a storing medium of an arbitraryformat such as RAM (Random Access Memory), a flash memory, ROM (ReadOnly Memory), EPROM (Erasable Programmable ROM), EEPROM (ElectronicallyErasable and Programmable ROM), a register, a hard disk, a removabledisk, and CD-ROM.

Such a storing medium is connected to the processor so that theprocessor can write and read information into and from the storingmedium. Such a storing medium may also be accumulated in the processor.Such a storing medium and processor may be arranged in anApplication-Specific Integrated Circuit or ASIC. Such ASIC may bearranged in the base station apparatus 200, the user equipment, and thesmall-node device 500. As a discrete component, such a storing mediumand processor may be arranged in the base station 200, the userequipment 100, and the small-node device 500.

Generally, according to one or more embodiments of the presentdisclosure, a device in a mobile communication system, in which a mobilestation communicates with a server, may include, at least, a 1stcommunication unit for communicating with a radio base station using afirst link, multiple 2nd communication units for communicatingwirelessly with the mobile station using a second link, a buffering unitfor buffering data, and a 3rd communication unit for communicating withthe server using a third link.

Additionally, the 1st communication unit exchanges with the radio basestation a first control signal for establishing the second link; themultiple 2nd communication units establish the second link on receivingthe first control signal, the multiple 2nd communication units receive afirst data in the second link which is sent by the mobile station to theserver, the 3rd communication unit transmit the first data to the serverin the third link, the 3rd communication unit receives a second datawhich is sent by the server to the mobile station, the multiple 2ndcommunication units transmit the second data to the mobile station, andthe buffering unit buffers the first data and the second data for themultiple 2nd communication units.

Thus, one or more embodiments of the present invention has beenexplained in detail by using the above-described embodiments. However,it is obvious that for persons skilled in the art, the present inventionis not limited to the embodiments explained herein. Specifically, thedescription of the specification is intended for explaining the exampleonly and does not impose any limited meaning to the present invention.

Abbreviations

LTE Long Term Evolution

PHY Physical

D2UE Device to UE

Macro2UE Macro to UE

UE User equipment

NAS Non Access Stratum

RRC Radio Resource Control

TDD Time Division Duplex

FDD Frequency Division Duplex

D2D Device to Device

CN Core Network

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

What is claimed is:
 1. In a cellular telecommunications network, amobile communication system to offload data traffic from radio basestations to small-node devices, comprising: at least onemacro-base-station-to-the-small-node-device (BS2D) communication sectionin communication with a radio base station through a first link; aplurality of small-node-device-to-user-equipment (D2UE) communicationsections in wireless communication with a mobile station through asecond link; a buffer section to buffer data; and a backhaulcommunication section in communication with a server through a thirdlink, wherein the BS2D communication section receives, through the firstlink, a first control signal from the radio base station to establishthe second link, wherein the plurality of D2UE communication sectionsestablish the second link upon receiving the first control signal,wherein the plurality of D2UE communication sections receive a firstdata through the second link which is sent by the mobile station to theserver, and wherein the backhaul communication section transmit thefirst data to the server through the third link, wherein the backhaulcommunication section receives a second data which is sent by the sewerto the mobile station, wherein the plurality of D2UE communicationsections transmit the second data to the mobile station, and wherein thebuffer section buffers the first data and the second data for theplurality of D2UE communication sections.
 2. The mobile communicationsystem of claim 1, further comprising: a center small-node devicecomprising the buffer section and the backhaul communication section;and a plurality of small-node devices configured to communicate with thecenter small-node device and the mobile station.
 3. The mobilecommunication system of claim 2, wherein the center small-node device isconfigured to: manage D2UE connections between the plurality ofsmall-node devices and the mobile station; and buffer data to betransmitted in downlink and data received in uplink for the plurality ofsmall-node devices.
 4. The mobile communication system of claim 2,wherein the radio base station notifies the center small-node device ofidentification numbers of each of the plurality of small-node devices ina small-node device group, and wherein the center small-node deviceselects one or more of the plurality of small-node devices in thesmall-node device group for communication with the mobile station,wherein the selection is made based on the quality of each associatedD2UE connection.
 5. The mobile communication system of claim 2, whereinthe buffer section in the center small- node device comprises multiplebuffer sections.
 6. The mobile communication system of claim 2, whereineach of the plurality of small-node devices includes one of theplurality of D2UE communication sections.
 7. The mobile communicationsystem of claim 2, wherein the plurality of small-node devices and thecenter small-node device each comprise a portion of the plurality ofD2UE communication sections.
 8. The mobile communication systems ofclaim 2, wherein the plurality of small-node devices handletransmitting1 receiving data in form of radio frequency signals, and thecenter small-node device handles baseband processing.
 9. The mobilecommunication systems of claim 2, wherein the plurality of small-nodedevices handle processing for physical layer, MAC layer and RLC layer,and the center small-node device handles processing for PDCP layer andbuffering data.
 10. The mobile communication system of claim 1, whereinat least one of the plurality of D2UE communication sections transmitthe second data to the mobile station at a time frame.
 11. The mobilecommunication system of claim 1, wherein the first data and the seconddata are scrambled by a sequence specific to the mobile station in thesecond link.
 12. The mobile communication system of claim 1, whereinidentification numbers of the plurality of D2UE communication sectionsare included in the first control signal.
 13. In a cellulartelecommunication network, a method to offload data traffic from radiobase stations to small-node devices, comprising: communicating with aradio base station through a first link with at least onemacro-base-station-to-the-small-node-device (BS2D) communicationsection; buffering data with a buffer section; communicating wirelesslywith a mobile station through a second link with a plurality ofsmall-node-device-to-user-equipment (D2UE) communication sections;communicating with a server through a third link with a backhaulcommunication section; receiving from the radio base station through thefirst link a first control signal to establish the second link at theBS2D communication section; establishing the second link upon receivingthe first control signal at the plurality of D2UE communicationsections; receiving at the plurality of D2UE communication sections afirst data through the second link which is sent by the mobile stationto the server, and wherein the backhaul communication section transmitthe first data to the server through the third link; receiving at thebackhaul communication section a second data which is sent by the serverto the mobile station, wherein the plurality of D2UE communicationsections transmit the second data to the mobile station; and bufferingwith the buffer section the first data and the second data for theplurality of D2UE communication sections.
 14. The method to offload datatraffic of claim 13, wherein communicating with the radio base station,the server, and the mobile station further comprises: communicating withthe server and radio base station using a center small-node devicecomprising the buffer section and the backhaul communication section;and communicating with the mobile station and the center small-nodedevice using a plurality of small-node devices.
 15. The method tooffload data traffic of claim 14, wherein the center small-node devicefurther comprises: managing D2UE connections between the plurality ofsmall-node devices and the mobile station; and buffering data to betransmitted in downlink and data received in uplink for the plurality ofsmall-node devices.
 16. The method to offload data traffic of claim 14,further comprising: notifying, with the radio base station, the centersmall-node device of identification numbers of each of the plurality ofsmall-node devices in a small-node device group; and selecting, with thecenter small-node device, one or more of the plurality of small-nodedevices in the small-node device group for communication with the mobilestation, wherein the selection is made based on the quality of eachassociated D2UE connection.
 17. The method to offload data traffic ofclaim 14, wherein the center small-node device further comprises:managing D2UE connections between the plurality of small-node devicesand the mobile station; and buffering data to be transmitted in downlinkand data received in uplink for the plurality of small-node devices, andthe method further comprising: notifying, with the radio base station,the center small-node device of identification numbers of each of theplurality of small-node devices in a small-node device group; andselecting, with the center small-node device, one or more of theplurality of small-node devices in the small-node device group forcommunication with the mobile station, wherein the selection is madebased on the quality of each associated D2UE connection.
 18. In acellular telecommunications network, a small-node device to offload datatraffic from radio base stations to the small-node device and acenter-small-node device, comprising: amacro-base-station-to-the-small-node-device (BS2D) communication sectionin communication with a radio base station through a first link; and asmall-node-device-to-user-equipment (D2UE) communication section inwireless communication with a mobile station through a second link;wherein the BS2D communication section receives, through the first link,a first control signal from the radio base station to establish thesecond link, wherein the D2UE communication section establish the secondlink upon receiving the first control signal, wherein the D2UEcommunication section receive a first data through the second link whichis sent by the mobile station to a server, and wherein the D2UEcommunication section transmit the first data to the center-small-nodedevice, wherein the center-small-node device transmit the first data tothe sewer through the third link, wherein the center-small-node devicereceives a second data through the third link which is sent by theserver to the mobile station, and wherein the center-small-node devicetransmits the second data to the D2UE communication section, wherein theD2UE communication section transmits the second data to the mobilestation through the second link, and wherein the center-small-nodedevice buffers the first data and the second data for the D2UEcommunication section.
 19. In a cellular telecommunications network, acenter-small-node device to offload data traffic from radio basestations to a plurality of small-node devices and the center-small-nodedevice, comprising: a buffer section to buffer data and to communicatewith a plurality of small-node devices; and a backhaul communicationsection in communication with a server through a first link, wherein theplurality of small-node devices communicate with a mobile stationthrough a second link, wherein the plurality of small-node devicesreceive a first data through the second link which is sent by the mobilestation to a server, and wherein the plurality of small-node devicestransmit the first data to the buffer section, wherein the backhaulcommunication section transmit the first data to the server through thethird link, wherein the backhaul communication section receives a seconddata which is sent by the server to the mobile station, and wherein thebuffer section transmits the second data to the plurality of small-nodedevices, wherein the small-node devices transmit the second data to themobile station, and wherein the buffer section buffers the first dataand the second data.
 20. In a cellular telecommunications network, amobile communication system to offload data traffic from radio basestations to small-node devices, comprising: at least onemacro-base-station-to-the-small-node-device (BS2D) communication sectionin communication with a radio base station through a first link; aplurality of small-node-device-to-user-equipment (D2UE) communicationsections in wireless communication with a mobile station through asecond link; a buffer section to buffer data; and a backhaulcommunication section in communication with a server through a thirdlink, wherein the BS2D communication section receives, through the firstlink, a first control signal from the radio base station to establishthe second link, wherein the plurality of D2UE communication sectionsestablish the second link upon receiving the first control signal,wherein the plurality of D2UE communication sections receive a firstdata through the second link which is sent by the mobile station to theserver, and wherein the backhaul communication section transmit thefirst data to the server through the third link, wherein the backhaulcommunication section receives a second data which is sent by the serverto the mobile station, wherein the plurality of D2UE communicationsections transmit the second data to the mobile station, and wherein thebuffer section buffers the first data and the second data for theplurality of D2UE communication sections.
 21. The mobile communicationsystem of claim 20, further comprising: a center small-node devicecomprising the buffer section and the backhaul communication section;and a plurality of small-node devices configured to communicate with thecenter small-node device and the mobile station.
 22. The mobilecommunication system of any of the proceeding claims 20 and 21, whereinthe center small-node device is configured to: manage D2UE connectionsbetween the plurality of small-node devices and the mobile station; andbuffer data to be transmitted in downlink and data received in uplinkfor the plurality of small-node devices.
 23. The mobile communicationsystem of any of the proceeding claims 20-22, wherein the radio basestation notifies the center small-node device of identification numbersof each of the plurality of small-node devices in a small-node devicegroup, and wherein the center small-node device selects one or more ofthe plurality of small-node devices in the small-node device group forcommunication with the mobile station, wherein the selection is madebased on the quality of each associated D2UE connection.
 24. The mobilecommunication system of any of the proceeding claims 20-23, wherein thebuffer section in the center small-node device comprises multiple buffersections.
 25. The mobile communication system of any of the proceedingclaims 20-24, wherein each of the plurality of small-node devicesincludes one of the plurality of D2UE communication sections.
 26. Themobile communication system of any of the proceeding claims 20-25,wherein the plurality of small-node devices and the center small-nodedevice each comprise a portion of the plurality of D2UE communicationsections.
 27. The mobile communication systems of any of the proceedingclaims 20-26, wherein the plurality of small-node devices handletransmitting/ receiving data in form of radio frequency signals, and thecenter small-node device handles baseband processing.
 28. The mobilecommunication systems of any of the proceeding claims 20-27, wherein theplurality of small-node devices handle processing for physical layer,MAC layer and RLC layer, and the center small-node device handlesprocessing for PDCP layer and buffering data.
 29. The mobilecommunication system of any of the proceeding claims 20-28, wherein atleast one of the plurality of D2UE communication sections transmit thesecond data to the mobile station at a time frame.
 30. The mobilecommunication system of any of the proceeding claims 20-29, wherein thefirst data and the second data are scrambled by a sequence specific tothe mobile station in the second link.
 31. The mobile communicationsystem of any of the proceeding claims 20-30, wherein identificationnumbers of the plurality of D2UE communication sections are included inthe first control signal.